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DEPLOYING RFID –
CHALLENGES, SOLUTIONS,
AND OPEN ISSUES
Edited by Cristina Turcu

Deploying RFID – Challenges, Solutions, and Open Issues
Edited by Cristina Turcu
Published by InTech
Janeza Trdine 9, 51000 Rijeka, Croatia
Copyright © 2011 InTech
All chapters are Open Access articles distributed under the Creative Commons
Non Commercial Share Alike Attribution 3.0 license, which permits to copy,
distribute, transmit, and adapt the work in any medium, so long as the original
work is properly cited. After this work has been published by InTech, authors
have the right to republish it, in whole or part, in any publication of which they
are the author, and to make other personal use of the work. Any republication,
referencing or personal use of the work must explicitly identify the original source.
Statements and opinions expressed in the chapters are these of the individual contributors
and not necessarily those of the editors or publisher. No responsibility is accepted
for the accuracy of information contained in the published articles. The publisher
assumes no responsibility for any damage or injury to persons or property arising out
of the use of any materials, instructions, methods or ideas contained in the book.
Publishing Process Manager Davor Vidic
Technical Editor Teodora Smiljanic
Cover Designer Martina Sirotic
Image Copyright Albert Lozano, 2010. Used under license from Shutterstock.com
First published August, 2011
Printed in Croatia
A free online edition of this book is available at www.intechopen.com
Additional hard copies can be obtained from orders@intechweb.org
Deploying RFID – Challenges, Solutions, and Open Issues, Edited by Cristina Turcu
p. cm.
ISBN 978-953-307-380-4

free online editions of InTech
Books and Journals can be found at
www.intechopen.com

Contents
Preface IX
Chapter 1 The Challenges and Issues Facing the
Deployment of RFID Technology 1
Peter Darcy, Prapassara Pupunwiwat and Bela Stantic
Chapter 2 RFID Components, Applications and System
Integration with Healthcare Perspective 27
Kamran Ahsan
Chapter 3 Development of a Neonatal Interactive
Simulator by Using an RFID Module
for Healthcare Professionals Training 51
Loreana Arrighi, Jenny Cifuentes, Daniel Fonseca,
Luis Méndez, Flavio Prieto and Jhon J. Ramírez
Chapter 4 RFID Technology in Preparation and
Administration of Cytostatic Infusions 83
Šárka Kozáková and Roman Goněc
Chapter 5 Application of RFID Technology in eHealth 103
Cristina Turcu, Tudor Cerlinca,
Marius Cerlinca and Remus Prodan
Chapter 6 RFID Technology and Multi-Agent
Approaches in Healthcare 127
Felicia Gîză, Cristina Turcu and Cornel Turcu
Chapter 7 Farm Operation Monitoring System with
Wearable Sensor Devices Including RFID 141
Tokihiro Fukatsu and Teruaki Nanseki
Chapter 8 The Application of RFID in Automatic
Feeding Machine for Single Daily Cow 159
Zhijiang Ni, Zhenjiang Gao and Hai Lin

VI Contents
Chapter 9 The U.S. National Animal Identification System
(NAIS) & the U.S. Beef-Cattle Sector:
A Post-Mortem Analysis of NAIS 167
Rhonda Skaggs
Chapter 10 Mine Planning Using RFID 179
Vladimir Konyukh
Chapter 11 The Applicability of RFID for Indoor Localization 203
Apostolia Papapostolou and Hakima Chaouchi
Chapter 12 Use of Active RFID and Environment-Embedded
Sensors for Indoor Object Location Estimation 219
Hiroaki Fukada, Taketoshi Mori, Hiroshi Noguchi
and Tomomasa Sato
Chapter 13 RFID Sensor Modeling by Using an
Autonomous Mobile Robot 237
Grazia Cicirelli, Annalisa Milella and Donato Di Paola
Chapter 14 Location of Intelligent Carts Using RFID 249
Yasushi Kambayashi and Munehiro Takimoto
Chapter 15 Services, Use Cases and Future Challenges for
Near Field Communication: the StoLPaN Project 265
Carlo Maria Medaglia, Alice Moroni, Valentina Volpi, Ugo Biader
Ceipidor, András Vilmos and Balázs Benyó
Chapter 16 RFID Applications in Cyber-Physical System 291
Nan Wu and Xiangdong Li
Chapter 17 SAW Transponder – RFID for Extreme Conditions 303
Alfred Binder, Gudrun Bruckner and René Fachberger
Chapter 18 Internetworking Objects with RFID 319
Rune Hylsberg Jacobsen, Qi Zhang and
Thomas Skjødebjerg Toftegaard
Chapter 19 Applying RFID Technology to Improve User
Interaction in Novel Environments 335
Elena de la Guía, María D. Lozano
and Víctor M.R. Penichet
Chapter 20 Building Blocks of the Internet of Things:
State of the Art and Beyond 351
Alexandru Serbanati, Carlo Maria Medaglia
and Ugo Biader Ceipidor

Contents VII
Chapter 21 RFID Security and Privacy 367
Michel Arnaud
Chapter 22 The Ethics of RFID Technology 377
Joël Schlatter and Fouad Chiadmi

Preface
Radio frequency identification (RFID) is a technology that is rapidly gaining
popularity due to its several benefits in a wide area of applications like inventory
tracking, supply chain management, automated manufacturing, healthcare, etc. The
benefits of implementing RFID technologies can be seen in terms of efficiency
(increased speed in production, reduced shrinkage, lower error rates, improved asset
tracking etc.) or effectiveness (services that companies provide to the customers).
Despite these numerous benefits, the technology has limited widespread
implementation, due to the insufficient robustness and reliability of the RFID
technology, cheaper alternatives to RFID (bar‐codes), the costs‐benefits balance of
RFID implementation and the absence of common standards and interoperability.
In these conditions, it is the researchers’ goal to contribute to the improvement of this
technology and the providing of new and valuable solutions to the industry personnel.
The book includes interesting research studies from experienced scientists in the RFID
domain.
In chapter 1, the authors present the importance of RFID and the shortcomings of the
current approaches designed to correct some issues among the integration of systems
including security, privacy, and data abnormalities. They also recommend solutions to
these issues.
Chapter 2 deals with the study of the RFID components such as antenna and reader. It
also discusses the RFID active and passive tags, and compares these tags, considering
both advantages and disadvantages of RFID system. RFID applications are explored
and a technical model is analyzed. The chapter also considers the healthcare
perspectives and RFID use within healthcare settings. This study outlines a model for
connected RFID applications, which provides quick support for various healthcare
functions and enhances flexibility for different systems’ components integration.
Chapter 3 outlines the experience and achievements attained in a project carried out
by the National University of Colombia. This project was intended to design and
implement RFID‐based tools for training students in medical and nursing techniques
applied on neonatal patients.

X Preface
The authors of chapter 4 propose an RFID‐based solution to reduce the human factor
in the preparation and administration of cytostatic infusions.
In chapter 5 the authors propose an RFID‐based system that integrates RFID and
multi‐agent technologies in health care in order to make patient emergency care as
efficient and risk‐free as possible, by providing doctors with as much information
about a patient and as quickly as possible. Also they describe a general purpose
architecture and data model that is designed for both collecting ambulatory data from
various existing devices and systems, and storing clinically significant information in
order to be accessed by the emergency care physician.
In chapter 6 the authors propose an RFID‐based multi‐agent system, that facilitates the
integration of data from heterogeneous sources in order to achieve a complete patient
electronic medical record. The adoption of this system does not require major changes
in terms of the software resources existing in the medical units.
In chapter 7 the authors propose a farm operation monitoring system using wearable
sensor devices with RFID readers and various sensing devices such as motion sensors,
cameras, and a GPS. This system recognizes detailed farming operations automatically
in various situations by analyzing the data from sensors and detected RFID tags. The
tags and sensors are attached to relevant objects such as farming materials, machinery,
facilities, and so on. In this chapter, the authors, based on their research, describe the
concept and features of this system and the results of several experiments conducted
on a prototype system. The major applications and extensions of the current systems
are also outlined.
In chapter 8, the authors introduce the application of RFID in day‐to day activity in
cow industry, regarding the use of RFID technology in automatic cow feeding
machine.
Chapter 9 focuses on the cow‐calf sector, with an overview of U.S. agriculture and the
beef‐cattle sector. Finally, the author presents what can be called “the National Animal
Identification System (NAIS) Pushback”.
In chapter 10 the author presents the new potential of RFID‐applications in mine
planning. An RFID‐based system can be used to visualize the placement of machines
inside roadways; to monitor miners with personal transponders; to prevent non‐
permitted control of machines; to prioritize the control of machines; to evaluate the
productivity of both machines and mining areas; to evaluate fuel consumption and
machine resources, etc. After being gathered, this information is used for the mine
management.
In chapter 11, the authors investigate the applicability of the RFID technology in
location sensing, the main design, and environmental factors that should be
considered before developing an RFID‐based localization scheme. The authors present
a scenario according to which the location of multiple reader‐enabled terminals need

Preface XI
to be estimated based on the information retrieved from low cost passive tags, which
are deployed in a particular area. Also, the authors propose a mathematical model for
taking into account all implicating factors which affect the accuracy performance of the
system, like types of collisions among its components, interference of materials, and
temporal environmental changes.
Chapter 12 analyzes an indoor object localizing method by using active RFID tags and
simple switch sensors embedded in the environment. The authors focus in their work
on object’s ʺlocationʺ in the environment (e.g. Table, Bed, Sofa, etc.) instead of object’s
3‐dimensional position, the only object location allowing the achievement of their
application.
In chapter 13, an approach for developing an RFID sensor model is presented. The
authors examine recent progresses in fuzzy logic‐based RFID sensor modeling using
an autonomous robot. Constructing a reliable sensor model is very important for
successive applications such as tag localization, robot localization, just to mention a
few.
Chapter 14 deals with optimizing distributed robotic control systems, considering as
example an intelligent cart system designed to be used in common airports. The
presented framework employs an RFID‐based localization algorithm and control
methods using mobile software agents.
In chapter 15 the authors present the services, use cases and the future challenges of
Near Field Communication, which is the most customer‐oriented one among RFID
technologies.
In chapter 16 the authors study a cyber‐physical system based on RFID technology.
They compare the proposed RFID system with a traditional wireless sensor network
system and discuss the applicability of the first one. Finally, the authors present the
design, methodology, and development of an active RFID‐based relative positioning
system, also showing the experimental results.
Chapter 17 gives an overview of SAW‐based RFID transponders made for extreme
conditions like temperatures up to 400°C or cryogenic temperatures down to –196°C.
The authors give an explanatory outline of SAW transponder function principles and
system performance, and also some application examples from steel and automotive
industries.
The chapter 18 discusses the RFID/WSN technology from a networking perspective.
The authors outline the development needed to integrate RFID systems with Internet
of Things and present the evolution from today’s connection of objects to the future
networking of objects.
Chapter 19 deals with the application of RFID technology to improve user interaction
in novel environments. The authors describe the development and implementation of

XII Preface
three different use cases, actually implementing the concept of context‐awareness,
location awareness, and Internet of Things.
Chapter 20 provides a historical and conceptual introduction to the IoT topic. The
work also outlines key aspects in the process of moving from the current state of the
art of IoT, where objects have digital identities, towards a network of objects having
digital personalities and being able to interact with each other and with the
environment. Finally, a selection of the possible impacts of the IoT is analyzed.
Chapter 21 address issues of the protecting privacy of RFID tag carriers in a “privacy
by design” model, which is described on four different levels: legal aspects, policy
services, technical specifications and security services.
The final chapter of this book goes beyond identification matters and addresses
aspects referring to the ethics of RFID technology. The author focuses on the ethical
approach that must be concerned with the subjectification of people through the use of
the technology.
Leading to considerable operational and strategic benefits, RFID technology continues
to bring new levels of intelligence and information, strengthening the experience of all
participants in this research domain, and serving as a valuable authentication
technology. We hope this book will be useful for engineers, researchers and industry
personnel, and provide them with some new ideas to address current and future
issues they might be facing.
Cristina TURCU
Stefan cel Mare University of Suceava
Romania

0
The Challenges and Issues Facing the
Deployment of RFID Technology
Peter Darcy, Prapassara Pupunwiwat and Bela Stantic
Institute of Integrated and Intelligent Systems, Griffith University
Australia
1. Introduction
Radio Frequency Identification refers to wireless technology that uses radio waves to
automatically identify items within certain proximity. This process involves tagging items
with a transmitter which will emit bursts of information including, but not limited to, the
identification of the tag. There are three main varieties of tags: Active, Semi-active and
Passive. Active tags rely solely on a battery for its power source resulting in the maximum
integrity rate and reading range but, also, a limited lifespan and higher cost. Semi-Active
tags use batteries to extend the range of the tag only resulting in a higher reading rate than
passive tags, a longer lifespan than the active tags, but also higher cost. The passive tag uses
the electromagnetic pulse from readers as a power source to transmit its identifier. Due to its
lack of a battery, passive tags are the most cost effective and theoretically have an unlimited
lifespan. However, due to their lack of the power source, passive tags also have a limited range
and produce the largest amount of data anomalies. The RFID Reader is used to interrogate
the zone to discover tags within proximity of the reader range. If a tag is discovered, its
identification along with the reader’s ID and the timestamp of the observation are recorded.
This information is then passed through the Middleware where initial filtration is done to
avoid data anomalies being recorded. Finally, the information will then be stored within a
database ready to be queried for future analysis.
Due to the benefits of the technology, RFID is currently employed in various commercial
sectors to provide automated assistance for mundane tasks. There are hospitals which have
employed tagged bracelets to ensure maximum care is given to surgical patients. At various
airports around the world, RFID is being utilised to track passengers’ bags to ensure that
the location of the luggage will be known at all times. In various cities around the world,
pets have had RFID chips implanted to ensure that, when lost, the authorities can find their
owners’ information by simple scanning the tag. Various countries have also introduced the
RFID-enabled toll system designed for cars at RFID-enabled toll booths which allow drivers
to continue on their journey and avoid the necessity of stopping to pay.
Despite the advantages gained from RFID technology integration, various drawbacks prevent
the wide-scale adoption into the majority of the commercial sector. There are three main
issues concerning the integration of the architecture. The first issue is security when using
the technology as tags are prone to various physical and virtual attacks upon the system.
The second concern stems from the need of privacy surrounding the data collected as the
observations recorded can be used for breaches in privacy. The third issue is that the
1

2 Will-be-set-by-IN-TECH
data collected among systems, in particular where passive tags are utilised, produces data
characteristics that make the systems harder to use.
With regard to the data characteristics issue of RFID, there are four main problems. The first is
that the data collected only contains two identifiers and a timestamp making the low-level
data useless without context of other information. The large amounts of data gained in
short periods of time is the second complication that arises from the use of RFID technology
resulting in the database storing massive amounts of observations, some of which are useless.
The third obstacle found among the integration of RFID systems is the complex spatial and
temporal dimensions resulting from handheld readers and other advanced devices. The final
difficulty is the tags generating ambiguous and incorrect observations resulting in duplicate,
wrong and missing anomalies.
Various methodologies have been mentioned in literature to address the current problems
with RFID data anomalies. We have categorised these solutions into three main groups:
Physical, Middleware and Deferred approaches. Various physical solutions have been
proposed in past studies to avoid missed readings in particular such as metallic-proof tag
pads, tag orientation and multiple tagging. Smoothing Filers and Anti-Collision Protocols are
Middleware solutions proposed to correct anomalies found within the Reader at the point of
scanning. Finally, there have been several rule-based and classification algorithms proposed
in past methodologies to be utilised at a deferred stage of the scanning cycle to correct various
anomalies already stored in the database.
Unfortunately, each of the proposed solutions has drawbacks that prevent it from eliminating
all problems found within RFID systems. With regard to the physical solutions, most
have been designed to eliminate a specific problem (i.e. the metallic padding) or it will
generate additional and unforeseen complications (multiple tags introducing duplicate reads).
Middleware solutions have been intended to be applied at the edge of the device when
the scanning is conducted which results in a limited amount of analytical information for
correction allowing ambiguous anomalies to persist. The Deferred approaches have the
advantage of having access to additional information in the database. However, they cannot
be applied in real-time and rely on user-specified rules or probabilistic algorithms that may
result in additional artificial anomalies.
We have examined RFID technology and its current uses in various applications. We
have also examined three core issues stopping the mass integration of RFID in the systems
including security, privacy and problematic data characteristics. We have further explored
the data characteristics issue to find that it contains low-level nature, large data gathering,
complex spatial and temporal aspects, and data anomalies. There have been various
methodologies proposed in the past to cope with the various data anomalies which we have
categorised into physical, middleware and deferred solutions. Unfortunately, due the various
drawbacks such as application-specified solutions, lack of analytical information or reliance
on user-specified/probabilistic algorithms, current approaches do not provide the adequate
support needed in RFID systems to be adopted in commercial sectors. In this work, we
have identified the importance of RFID, the shortcomings of existing approaches designed
to correct its issues, and have recommended solutions to these methodologies.
2. Radio Frequency Identification
Radio Frequency Identification (RFID) has had a long history commencing with its utilisation
during the Second World War to its modern usage. The basic architecture of RFID itself
2 Deploying RFID – Challenges, Solutions, and Open Issues

The Challenges and Issues Facing the Deployment of RFID Technology 3
Fig. 1. The timeline of recent RFID history from the 1940s through to the present day (Landt,
2001).
consists of a tag, reader and middleware to perform advanced analysis on the data which
makes it practical for use in many applications with beneficial outcomes. There are several
problems which arise when using the passive tags due to the nature of the system, in
particular, the amount of unreliable readings in the raw data.
2.1 History of RFID
For a general overview of RFID’s historical achievements, please see the timeline illustrated
in Figure 1. The physical birth of RFID would not come until the fusion of two technologies
was achieved approximately around the era of the World Wars. The first technology was the
Continuous Wave radio generation which was created in 1906 by Ernst F. W. Alexanderson.
The second technology was the Radar device which is thought to have been developed in
1922 and was utilised extensively in World War II (Landt, 2001). The combination of these
two devices resulted in the concept of RFID which was first academically proposed in theory
by Harry Stockman in 1948. During this time, RFID was employed as a means to distinguish
between enemy and allied aircrafts in the war. Unfortunately, as Stockman notes, technology
had not progressed to the point that the complete potential of RFID technology could be
realised (Stockman, 1948).
RFID research continued to be pursued in both the academic community and the military
aircrafts’ division who were attempting to develop “Identification Friend or Foe” (IFF)
technology throughout the 1950s. It was not until the late 1960s that a Sensormatic and
Checkpoint developed the first commercial RFID product in the form of EAS or “Electronic
Article Surveillance” which consisted of a security system incorporating RFID tags that only
stored an “on or off” command to prevent theft in stores. RFID’s focus throughout the 1970s
was in the tracking of animals and vehicles and, also, within the automation of factories. This
adoption of the technology eventually led to the first RFID integrated road toll which was
established in Norway in 1978. It was employed later in various other locations world-wide,
the second notable one having been set up in 1989 at the Dallas North Turnpike in America
(Landt, 2005).
In the 1990s, RFID had been integrated into people’s daily activities. An example of this
includes the utilisation of RFID key cards for enhanced security to enable a higher level of
integrity for secure locations (Chawathe et al., 2004). In its most recent history from 2000-2010
and onwards, RFID has received the majority of its attention from various commercial sectors
adopting its technology (Derakhshan et al., 2007). Some of these industries include Wal*Mart
(Engels, 2005) where it has been used to enhance the supply chain, the US Department of
3
The Challenges and Issues Facing the Deployment of RFID Technology

Fig. 2. The flow of information between the different components of the RFID System
Architecture
Defence which has developed smarter tags (Collins, 2005) and the Aviation Industry which
attaches tags to identify different parts when shipping out items (Collins, 2004). For a more
comprehensive analysis of current RFID applications please see Section 3.
2.2 System Architecture
The System Architecture of an RFID system contains four important components (Chawathe
et al., 2004): an RFID Tag, an RFID Reader, the RFID Middleware and the Database Storage.
For a diagram representing the flow of information in this System architecture, please see
Figure 2.
The RFID Tag is the simplest, lowest level component of the RFID System Architecture. These
tags come in three types - Passive, Semi-Passive and Active. The Tag itself is made up of three
different parts: the Chip which holds the information the tag is to dispense, the Antenna
which is used to transmit the signal out and the Packaging which houses the Chip and
Antenna and may be applied to the surface of other items. The Passive Tags are the most
error-prone, but due to not needing a battery, also the most cost-effective and long-lasting.
Electromagnetic pulses emitted from the Readers allow the Passive Tag enough energy to
transmit its identification back. In comparison, the Semi-Passive Tag has a battery. However,
it is only utilised to extend the readability scan resulting in a shorter life-span but increased
observation integrity. The final tag is the Active Tag which utilises a battery to, not only extend
its range, but also to transmit its identification number. From its heavy reliance of the battery,
the Active Tag has the highest cost and shortest life-span of all the tags currently available
(Chawathe et al., 2004). Even today, there are novel and emerging technologies to reduce the
production cost even further such as the Chipless RFID System Tags and Readers (Preradovic
et al., 2008; Preradovic & Karmakar, 2009).
The RFID Readers are the machines used to record the Tag identifiers and attach a timestamp
of the observation. It does this by emitting a wave of electromagnetic energy which then
interrogates the Tags until they have responded. These devices have a much greater purpose
when needing to interrogate Passive and Semi-Passive Tags as they also provide the power
necessary to transmit the information back. Readers, like the Tags, come in a variety of types
such as the Hand-held reader and the Mounted Reader. The mobile hand-held tags are used
for mainly determining which objects are present within a group, for example, when needing

Fig. 3. The various parts of a Electronic Product Code (EPC) stored on RFID Tags.
to stocktake several items within a supermarket. In comparison, the Mounted Readers are
static in geographical locations and used primarily to track items moving through their zones
such as mounted readers to observe all items on a conveyer belt.
The Middleware, also commonly known as the Savant or Edge Systems, is the layer at which
the raw RFID readings are cleaned and filtered to make the data more application-friendly.
It receives information passed into it from the Readers and then applies techniques such as
Anti-Collision and Smoothing Algorithms to correct simple missing and duplicate anomalies
(Jeffery et al., 2006; Shih et al., 2006). The filtrated observational records, including the Tag
and Reader Identifiers along with the Timestamp the reading was taken, are then passed onto
the Database Storage.
The final destination of all the observational records is to be placed within a collection of
readings taken from all connected RFID Readers. This component is known as the Database
Storage and is used to hold all information which is streamed from the Readers. In most cases,
due to the massive amount of interrogation undertaken to read all Tags at all times, this can
result in massive floods of data, for example, 7TB of data generated daily (Schuman, 2005).
Having all information stored in a central database also allows for higher level processes such
as data cleaning, data mining and analytical evaluations.
EPC Reader Timestamp
030000E500023C000431BA3 001 2008-07-29 14:05:08.002
030000E500023C000431BA3 003 2008-07-29 14:32:12.042
030000E500023C000431BA3 002 2008-07-29 14:45:54.028
030000E500023C000431BA3 004 2008-07-29 15:02:06.029
030000E500023C000431BA3 007 2008-07-29 15:18:49.016
Table 1. A table populated with sample RFID Data containing the information of EPC,
Reader and Timestamp.
2.3 Format of observations
The format of the data recorded in the database after a tag has been read consists of three
primary pieces of information: the Electronic Product Code, the Reader Identifier which made
the observation, and the Timestamp which contains the time the reading occurred. Table 1
contains information typically found stored in the Database Storage.
The Electronic Product Code (EPC) is a unique identification number introduced by the
Auto-ID Center and given to each RFID Tag which is made up of a 96 bit, 25 character-long
code containing numbers and letters. The number itself, as seen in Figure 3, is made up of
a Header for 8 bits, EPC Manager for 28 bits, Object Class for 24 bits and Serial Number for
36 bits (Ward et al., 2006). Ward and Kranenburg state that a possible alternative to using the
5

EPC is to employ IPv6 which is the advanced version of internet addresses. These will take
over the current system which is IPv4 (Ward et al., 2006). It is estimated that, since IPv6 will
have 430 quintillion internet addresses as opposed to the current 4 billion address limit, there
will be enough addresses for all items being tracked with RFID.
The EPC Class 1 Generation 2 is widely used in the Ultra High Frequency (UHF) range for
communications at 860-960MHz. The passive RFID tag is sometime referred to as EPC Gen-2
tag, where the standards have been created by EPCGlobal (EPCGlobal, 2006), (EPCGlobal,
2005), (EPCGlobal, 2008). The most common encoding scheme with 96 bits encoding currently
used includes: the General Identifier (GID-96), the Serialised Global Trade Item Number
(SGTIN-96), the Serialised Shipping Container Code (SSCC-96), the Serialised Global Location
Number (SGLN-96), the Global Returnable Asset Identifier (GRAI-96), the Global Individual
Asset Identifier (GIAI-96), and the DoD Identifier (DoD-96).
In order to manage and monitor the traffic of RFID data effectively, the EPC pattern is usually
used to keep the unique identifier on each of the items arranged within a specific range.
The EPC pattern does not represent a single tag encoding, but rather refers to a set of tag
encodings. For instance, the General Identifier (GID-96) includes three fields in addition to
the ‘Header’ with a total of 96-bits binary value. 25.1545.[3456-3478].[778-795] is a sample
of the EPC pattern in decimal, which later will be encoded to binary and embedded onto
tags. Thus, within this sample pattern, the Header is fixed to 25 and the General Manager
Number is 1545, while the Object Class can be any number between 3456 and 3478 and the
Serial Number can be anything between 778 and 795.
Within each EPC, the Uniform Resource Identifier (URI) encoding complements the EPC Tag
Encodings defined for use within RFID tags and other low-level architectural components.
URIs provide an information for application software to influence EPC in a way that is
independent of any specific tag-level representation. The URI forms are also provided for
pure identities, which contain just the EPC fields which are used to distinguish one item from
another. For instance, for the EPC GID-96, the pure identity URI representation is as follows:
urn:epc:id:gid:GeneralManagerNumber.ObjectClass.SerialNumber
In this representation, the three fields GeneralManagerNumber, ObjectClass, and
SerialNumber correspond to the three components of an EPC General Identifier (EPCGlobal,
2008). There are also pure identity URI forms defined for identity types corresponding to
certain encodings, the URI representations corresponding to these identifiers are as shown in
Table 2.
Encoding Scheme Uniform Resource Identifier
GID urn:epc:id:gid:GeneralManagerNumber.ObjectClass.SerialNumber
SGTIN urn:epc:id:sgtin:CompanyPrefix.ItemReference.SerialNumber
SSCC urn:epc:id:sscc:CompanyPrefix.SerialReference
SGLN urn:epc:id:sgln:CompanyPrefix.LocationReference.ExtensionComponent
GRAI urn:epc:id:grai:CompanyPrefix.AssetType.SerialNumber
GIAI urn:epc:id:giai:CompanyPrefix.IndividualAssetReference
DoD urn:epc:id:usdod:CAGECodeOrDODAAC.serialNumber
Table 2. The Uniform Resource Identifier encoding complements the EPC Tag Encodings
defined for use within RFID tags and other low-level architectural components
An example encoding of GRAI is demonstrates as follows:
urn:epc:id:grai:0652642.12345.1234

Fig. 4. An example RFID scheme which could be used to house the captured information
generated from a RFID system.
From the above example, the corresponding GRAI is 06526421234581234. Refereing to Table
2, the CompanyPrefix, AssetType, and SerialNumber of GIAI are represent as 0652642, 12345,
and 1234 respectively.
The Reader Identifier attribute is the unique identifier of the Reader so that the analyser will
be informed of which reader took the EPC reading. If the Reader is static in its location as well,
such a position of the reading may be derived from a simple query in the database later using
this value. Knowledge of the geographical location of each unique Reader identifier may also
provide additional information needed in future business processes.
The Timestamp contain a temporal reading used to identify the date and time that the Tag
passed within vicinity of the Reader. For example, 2008-07-29 14:05:08.002 would be stored as
a timestamp.
2.4 Storage of RFID data
In its rawest form, RFID data is recorded in a temporal stream of data consisting of EPC,
Reader and Timestamp. After the burst of information is recorded from the reader, the RFID
Savant or RFID Middleware modifies data to represent a higher level description of the events
that took place. For example, the Siemens RFID Middleware extracts the data and loads it into
a Dynamic Relationship Entity Relationship Model (Wang & Liu, 2005). Figure 4 depicts the
Entity Relationship Diagram (ERD) used as a basic Database Storage for RFID events. As seen
in the diagram, there are three prime entities that must be known, the Object, the Reader,
and the Location of the Reader. Each entity has an identifying tuple attached including the
Observation weak entity that also attaches the timestamp of a recorded event. Additionally,
more advanced systems will only record the start and end time that an Object is within a
Location, thereby saving memory so that observations are not recorded as frequently (Wang
et al., 2010).
7

Fig. 5. The various stages taken when transporting various RFID-enabled items in a supply
chain.
2.5 RFID advantages
The main advantage of RFID technology is that it is not necessary to have a line-of-sight
between the object and the reading device (Derakhshan et al., 2007). In comparison to object
scanners currently employed in various commercial sectors such as supermarkets, an object
is needed to be taken out, place on a conveyor belt, rotated until the barcode is within
the position and then placed back into the shopping trolley. If RFID is employed within
this scenario, all items would automatically be recorded when the customer approaches the
register and the cost tallied in one scan without the need of moving the items outside the
trolley, thus saving the company time, money and physical labour. Specifically in relation
to Passive Tags, there are two main advantages found when integrating RFID technology
(Chawathe et al., 2004). The first is that the manufacture of the RFID Passive tag is extremely
cheap. It is estimated that it only costs 5 cents per tag when bought in bulks of billions. The
second advantage of the Passive RFID System is that, due to the ingenuity of the tag itself, it is
not application-specific and may be applied to almost any domain. With regard to the variety
of uses of RFID, as stated by Polniak - “Uses of automatic identification are manifold, limited
only by one’s imagination” (Polniak, 2007).
3. Current uses of RFID
From investigating the current uses of RFID, we have discovered that each utilisation may be
placed into two different categories of RFID applications. The first, which we have labelled
“RFID Integrated Applications”, includes already existing systems which have been enhanced
and made more effective and efficient using RFID technology. We have labelled the second
category “RFID Specific Applications” in which prototype machines have been built from the
bottom-up to incorporate RFID technology in its very make up.

3.1 Integrated RFID Applications
We have defined Integrated Applications as scenarios in which originally existing business
operations have been augmented with the integration of RFID technology. The most common
use of RFID integrated applications is the generic supply-chain example of RFID integration
commonly employed by commercial stores such as Wal-Mart. In the example illustrated in
Figure 5, tagged Objects (T1-T9) are added to specific Pallets (P1-P3), which are then loaded
onto a Truck. The Truck will then transport the Pallets to their Warehouse destination at which
point the items are then packaged for display at their retail stores. Additionally, as described
by Derakhshan, Orlowska and Li, there are several other applications which have integrated
RFID technology into their business models (Derakhshan et al., 2007) such as:
• Defense and Military: The US Department of Defence (DOD) is investigating a new active
tag which has the ability to access and communicate via satellites. This new tag, known
as the “Third Generation Radio Frequency Identification with Satellite Communications
(3G RFID w/SATCOM)”, is expected to be used to increase the visibility of the DOD’s
supply chain and, in turn, increase the confidence of shipments to various war-torn regions
(Collins, 2005).
• Postal Package Tracking: The postal service has been found to incorporate RFID
world-wide with the primary goal of increasing the effectiveness of tracking packages and
parcels thereby increasing customers’ property security (Harrop, 2005).
• Aviation Industry: Two major aircraft manufacturers, Boeing and Airbus, have started
ensuring that the supplying factory parts for the aircraft use RFID tags for identifications
resulting in an easier process to locate and identify needed parts (Collins, 2004).
• Health Care: The Taiwanese Chang-Gung Memorial Hospital has been monitoring
surgical patients with RFID wristbands in order to ensure maximum care is given where
needed. The features available in the wristbands include the ability to decrypt data, obtain
read-only static fields (such as blood-types) and read/write dynamic fields which may be
updated and modified by medical staff (Swedberg, 2005).
• Baggage/Passanger Tracing: The Boston Logan International Airport and the Boston
Engineering Inkode Corporation have integrated RFID technology within the Secure
Environment for Airport Terminal Systems (SEATS) which passengers and their baggage
with passive RFID tags to track all movements from their arrival at the airport to boarding
the flight (Ferguson, 2005). This technology ensures not only that passengers will be able
to make their flight easier, but that their baggage location will always be known.
3.2 Specific RFID applications
We have categorised applications specifically designed and built with the integration of
RFID technology as Specific Applications. Four such examples which have been developed
in the recent years include the Magic Medicine Cabinet, the Multipurpose Smart Box, the
Augmentation of Desktop Items and the Smart Shelves (Brusey et al., 2003; Floerkemeier,
2004).
The Magic Medicine Cabinet, as described in (Wan, 1999), is a bathroom cabinet which is
used to assist in bridging the gap between the informational and physical aspects of the
medical world. The Magic Medicine Cabinet will allow RFID based tracking systems to
describe the content of what is being placed into and removed out of storage by the user.
Through a combination of Facial Recognition, Vital Sign Monitors, Voice Synthesisers and
9

RFID technologies, the Cabinet can intelligently decide whether or not the person currently
interacting with it should be taking the medicine. This, in turn, would being the action to the
owner’s attention if necessary.
As discussed in (Floerkemeier et al., 2003; Lampe & Floerkemeier, 2004), an automatic content
monitoring application called the “Smart Box”, similar to the Magic Medicine Cabinet, has
been designed to monitor the RFID-enabled contents placed inside. The Smart Box may also
be set up in different configurations to suit the context to which it will be applied such as a
Smart Surgical Kit for hospitals and a Smart Toolbox for mechanics (Floerkemeier et al., 2003).
The Augmentation of Desktop Items is a means of combining physical objects with virtual
interfaces using the inexpensive power of RFID tags and readers (Want et al., 1999). In a
typical scenario, an office object such as a book would be tagged and then read by a Reader
connected to a computer to allow the user additional functionality. For example, when
someone scans a book by the reader, the computer would use stored information relating to
the office to identify the book’s title and would begin to provide additional internet-features
such as summaries, discussions or would allow the user to order the book from Amazon.com.
The Smart Shelf is an RFID enabled device which tracks all items placed on it to accurately
determine the location of the said object (Decker et al., 2003; TecO & SAP/CEC, 2003). The
Smart Shelf was designed specifically with the secondary goal of obtaining the unobserved
events of a person handling an item at retail outlets and, subsequently, returning it to the
shelf thereby allowing business analysts further glimpses into the decision-making of the
consumers. From this information, it would be possible to detect if a shopper mentally debates
over the decision to purchase the product.
4. RFID issues
Before RFID can be utilised to its maximum potential, as opposed to the fraction in which
it is currently employed, certain issues need to be understood by the users, and corrected if
possible. The three core obstacles include the concerns of security, the problems surrounding
the privacy of the data captured and the characteristics associated with the nature of RFID.
Additionally, we will further examine the specific problems associated with anomalies present
within the captured observational records which are regarded as a characteristics of RFID.
When all of these issues are rectified to provide maximum security, privacy and integrity,
RFID will be able to realise its full potential in massive wide-scale adoptions.
4.1 RFID security
The issues associated with RFID Security, also known as Intrusion Detection, refers to the
discovery of foreign attacks upon the system usually utilising the tags that hinder the overall
integrity of the data. The following five issues are some of the most dominant with regard to
RFID security (Mitrokotsa et al., 2010; Thamilarasu & Sridhar, 2008):
• Eavesdropping: The act of setting up an additional reader to record tag data.
• Unauthorised Tag Cloning: Copying tag data onto an additional tag to gain the same
privileges.
• Man-in-the-Middle (MIM) Attack: When an external object pretends to be either a tag or
reader between actual tags and readers.
• Unauthorised Tag Disabling: When an external reader disables a tag not allowing it to be
utilised again.

• Unauthorised Tag Manipulation: Manipulating the tag data using an external reader.
Until these security issues existing in the current architecture, it becomes difficult for facilities
to employ RFID as a means of combatting unauthorised actions such as safe-guarding
sensitive or expensive objects or restrict personnel access into various locations. Currently,
there are techniques and approaches such as Tag Deactivation and Encryption (Karygiannis
et al., 2007), Mutual Authentication (Konidala et al., 2007), Detections in Tag Ownership
(Mirowski & Hartnett, 2007), Reader Analysers (Thamilarasu & Sridhar, 2008) and certain
data cleaners (Darcy, Stantic, Mitrokotsa & Sattar, 2010) to reduce the difficulties associated
with RFID Security.
4.2 RFID privacy
Privacy within the context of an RFID-enabled facility refers to either unknowingly
releasing critical information (deriving specific knowledge or tracking meaningless data)
(Langheinrich, 2009), or compiling a list of all items currently found on a person (Juels, 2006).
There have been several methodologies proposed in the past to ensure maximum privacy of an
individual, including the general approaches of Encrypting/Rewriting and Hiding/Blocking
Tags (Langheinrich, 2009). In addition to these general solutions, there have been more specific
and advanced approaches suggested such as killing/sleeping the Tags, carrying around a
privacy-enforcing RFID device, releasing certain information based solely on distance from
the reader and introducing Government Legislations (Juels, 2006).
4.3 RFID characteristics
There are certain characteristics associated with the nature of RFID technology (Cocci et al.,
2008; Derakhshan et al., 2007). These challenges include Low Level Data, Error-Prone Data,
High Data Volumes and its Spatial and Temporal Aspects. Low Level Data refers to the raw
observational readings being taken by the RFID Reader; Error-Prone Data is the problem
which RFID has with capturing the data; High Data Volumes refers to the ongoing obstacle
with managing exponential RFID data streams and Spatial and Temporal Aspects alludes to
the aspects of RFID’s freedom in being capable of being used in all situations.
As previously discussed in Section 2.3, the format of the data at the time of scanning is very
low level and lacks crucial information needed later for analysing the information captured.
The core problem with these observations is the lack of associations between the readings and
other information such as what the tags are attached to or the locations of the readers thereby
making captured data useless on its own. Humans must find significant information extracted
from these low level observations such as high level RFID Events (Khoussainova et al., 2007)
which are the transformed state of the raw readings into meaningful milestones. For example,
if a certain tag “202” is read at the reader “794” at timestamp “25/05/08 07:30:04”, there is not
enough information to comprehend the significance of the observation. By using relational
information such as reader locations and tag information, these low level observations may
be transformed into a high level event depicting the person named John being at the Front
Door of location at 7:30:04 on the 25/05/08.
RFID Data integrity is constantly lowered to the point of questioning its authenticity especially
when utilising passive tags due to errors captured within the observational data. These errors
include Missed Reads in which a tagged item is present but not recorded, Wrong Reads in
which data is captured where it should not resulting in the data set not reflecting events which
are actually taking place, and duplicate reads in which a tagged item is stored twice in the
11

database where it should only be stored once. Section 4.4 further expands the error-prone
nature of RFID where an analysis together with each of these errors are given.
Due to the continuous stream of information and the need to constantly interrogate tags,
readers record massive amounts of data over long periods of time. It has been estimated
that Wal*Mart currently generates about 7TB of information daily due to its RFID integration
(Raskino et al., 2005). Additionally, it is estimated that by the year 2015, with a steady increase
of RFID presence but lack of content management of the data generated, the information
collected will be a serious problem for integrated systems. This may ultimately lead to
a decrease of RFID usability and waste of information already gained unless either the
management of data collected is properly attended to or the technology currently employed
greatly increases its storage capacity.
As previously discussed in Derakhshan et al. (2007); Wang & Liu (2005), the exponential
growth of smaller hardware RFID solutions coupled with the cost reduction in manufacturing
these units results in RFID applications becoming increasingly dynamic in both spatial and
temporal properties. For example, there are hand-held RFID Readers which are carried by
people to scan groups of RFID tags in various locations. However, these scans will never be
able to be placed into a geographical context thus limiting the potential of analytical processes
that may be performed. Unless properly managed, the dynamic properties of RFID’s spatial
and temporal aspects may result in increasingly complex ambiguity ultimately resulting in
the data losing signiﬁcance, context and usability.
4.4 RFID anomalies
RFID observational data suffers from three main anomalies which are recorded with the
correct RFID readings. The ﬁrst is a Wrong Reading in which data is captured where it should
not be. The second is Duplicate Readings in which a tag is observed twice rather than once.
The third is the Missed Readings which occur when a tag is not read when and where the
object it is attached to should have been physically within proximity. Figure 6 contains an
example of a RFID-enabled shelf which has also generated the three anomalies, the recorded
data may be seen in Table 3.
What is Recorded
Tag EPC Timestamp Reader ID
T1 13/10/2010 14:31:05 R1
T2 13/10/2010 14:31:05 R3
T3 13/10/2010 14:31:05 R3
T3 13/10/2010 14:31:05 R4
T3 13/10/2010 14:31:05 R5
What is meant to be Recorded
Tag EPC Timestamp Reader ID
T1 13/10/2010 14:31:05 R1
T2 13/10/2010 14:31:05 R2
T3 13/10/2010 14:31:05 R3
T4 13/10/2010 14:31:05 R5
Table 3. The recordings that took place from the example in Figure 6 and the observations
that should have been recorded.
Wrong Readings, also known as Unreliable Readings or Ghost Reads falling into the False
Positives category, refer to observations found in the data storage of tag which were not
physically present in the location or time. These false readings may be produced when

Fig. 6. A graphical representation of a RFID-enabled bookshelf with the data anomalies that
may occur highlighted.
tags outside the normal Reader range are captured or where there is a problem with the
environmental setup (Bai et al., 2006). As discussed previously (Embry, 2005; Engels, 2005),
this problem has been identiﬁed as one of the two main technical problems with RFID. It
may also result in additional unnecessary labor to continually monitor the objects where the
locations of the tagged items is vital to the business process, for example, the tracking of
livestock. Within the example in Figure 6 and Table 3, Tag T2 is read by Reader R3 when in
reality it is closer to the area which should be scanned by Reader R2.
Duplicate Readings refer to an RFID tag which has been scanned twice in the database as
opposed to just one scanning. Like the Wrong Readings, Duplicate anomalies also fall into the
category of False Positive observations as they record the data which do not accurately depict
reality. This may occur in several situations such as the situation in which there is more than
one Reader covering an area and a tag happens to pass within overlapped region (Carbunar
et al., 2005). This can be hazardous and redundant as the tag is represented in two areas
during the same time period. Other duplicate reading situations occur when a scanned item
stays in the reader range for a long period of time or when the owners of the RFID system
attach multiple tags in order for an item to enhance its read rate (Bai et al., 2006). Ultimately,
not only does this anomaly cause contradicting observations where tags may appear in two
locations at the same time but it also leads to memory being wasted where it could be utilised
to store factual information. In the sample scenario depicted in Figure 6 and Table 3, Tag
13

T3 is captured by not only the correct Reader R3, but also R4 and R5 resulting in T3 having
duplicate entries in the recorded data set.
Missed Readings, also known as False Negative observations, refers to tagged objects not
being scanned when, in actuality, they were present. The exact percentage of tags that are read
remain only at 60%-70% under certain circumstances (Floerkemeier & Lampe, 2004). Reasons
for these anomalies stem from problems such as Tag Collisions, Tag Detuning, Water/Metal
Interference and Misalignment of the Tags. The missed reads anomaly has been identified
as the second major problem in RFID deployment by an array of researchers (Engels, 2005;
Floerkemeier & Lampe, 2004; Rahmati et al., 2007). The result of this anomaly may cause
the users to believe that all items which are meant to be present are not, thereby hindering
the overall process it was designed to make more efficient. Tag T4 in the example Figure 6 is
shown to be a missed read due to it being placed slightly outside the scanning range of Reader
R5 resulting in it not being recorded with the other tags in Table 3.
5. Current state-of-the-art approaches
In this section, we will provide a brief summary of all the current state-of-the-art approaches
we have investigated to correct the RFID issues. We have divided the methods into three
categories: Physical Approaches in which methods attempt to correct RFID anomalies
by improving the environment around the scanners, Middleware Approaches in which
algorithms attempt to correct the anomalies at the time of capturing and Deferred Approaches
which attempt to correct RFID data when it is stored in the Database. Table 4 provides a list of
each of the techniques examined in this section and the Corrected and Potentially Generated
Anomalies.
Methodology
Anomalies Corrected Anomalies Generated
Wrong Duplicate Missed Wrong Duplicate Missed
Physical
Tag Orientation - - X X - -
Weighing - X X - - -
Multiple Tags/Cycles - - X X X -
Eccopad - - X - - -
Middleware
Edge Filtering X X X X X X
Anti-Collision - - X - - -
Thresholds - - X1 - - -
Statistical Approx. X X X X X X
Deferred
P2P Collaboration X X X - - -
Proximity Detection X - X - - -
Cost-Conscious Cleaning X X X X X X
Data Mining Techniques X X X X X X
Probabilistic Inference - - X X - -
Event Transformation X X X X X X
Intelligent Classifiers X X X X X X
Table 4. A table depicting which anomalies are corrected and generated by the various
methodologies proposed. The ‘X’ denotes where the methodology either corrects or
generates the anomaly. Note1: The Thresholds methodology does not actually correct the
missing data but, rather, alerts the user to a False-Negative anomaly.

5.1 Physical approaches
One common solution to improve the tag reads in RFID systems is to employ Physical
Approaches. This enhances the environment where the scanning is conducted. We deﬁne
Physical Approaches as any solution which requires interaction with the equipment as
opposed to virtual interaction used at the middleware or at a deferred warehouse stage to
correct the captured data.
Rahhmati, Zhong, Hiltunen and Jana have conducted a study into the effects of reader rate
when positioning the RFID tag in different positions (Rahmati et al., 2007). The research found
that the Reader may scan the tags on an object most effectively when the Tag is positioned at
the front.
Potdar, Hayati and Chang have formulated a novel and simple solution designed to detect
missing RFID tags through the use of weights (Potdar et al., 2007). This method was created
for applications in situations in which items are required to be tracked while being transported
to various venues. It requires all tagged items to be weighed at the start of the transportation
route. The items are then weighed at the end of the trip to determine any difference in the
cargo weight. The system will determine if there are any missed reads coupled with an
attempt to ﬁnd any missing weight. If there are missing readings but a constant weight, the
system will scan the cargo again until all items have been recorded.
As described by both (Bai et al., 2006; Vogt, 2002), a common solution to deal with RFID
anomalies is to either install multiple readers or to attach multiple tags. Multiple readers are
installed in the environment in an attempt to enhance the reader rate by covering a more
substantial amount of ground. Another method of dealing with the enhancement of the read
rate is to attach multiple tags housing identical EPC numbers to the same object in an effort
for at least one of these tags to be read by the reader. Unfortunately, drawbacks arise from
both methods in the form of duplicate readings and tag collision occurrences.
Emerson & Cuming Microwave Products (Emerson & Cuming Microwave Products, 2008)
provides a device known as the Eccopad which is designed to enhance the reading rate
of tags placed on metal. As described in (Floerkemeier & Lampe, 2004), metallic objects
within a certain proximity will affect the reading potential of a passive RFID tag causing
missed readings. The Eccopad insulates the RFID tag in a discrete manner which enables the
maximum potential reading rate with little or no change in the spatial properties occurring.
5.2 Middleware approaches
Middleware Approaches refers to employing an algorithm to eliminate anomalies found in
systems to correct the data before storing it. This can refer to any program used at the
middleware stage of the RFID capture cycle to correct the raw incoming streamed data.
Edge Filtering refers to the cleaning being completed at the edge of the RFID system, that is,
at the point of raw observations being read. Jeffery, Garofalakis and Franklin have proposed
a method analysing the usage of an adaptive sliding window to correct unreliable readings
within an RFID system (Jeffery et al., 2006). A sliding window is used to smooth out the raw
data in order to accommodate both false positive and false negative readings. The problem
associated with this technique is that the result of utilising a small sliding window will be false
negatives whereas the large window may result in false positives being introduced. Thus,
Jeffery et al, proposed a solution to create a declarative and adaptive smoothing window
named SMURF (Statistical sMoothing for Unreliable RFid data) which they have continually
improved (Jeffery et al., 2008).
15

RFID Anti-collision protocols are algorithms used at the edge to avoid missed readings. When
an RFID scan is performed on several RFID tags, there are many relaying messages sent back
and forth between the tag and the reader. If there are a large number of tags to be scanned
in a certain read, these messages may collide in the air between their source and destination
resulting in the information not arriving at the correct time if at all. Certain protocols are also
designed to handle other forms of hazards such as instances where readers placed within a
certain proximity interfere with each other’s interrogation cycle causing collisions (Shih et al.,
2006).
The various types of anti-collision methods for collision can be reduced to two basic types:
probabilistic and deterministic methods. In a probabilistic method, tags respond at randomly
generated times. If a collision occurs, colliding tags will have to identify themselves again
after waiting for a random period time frame. From past literature, there have been several
methods proposed such as: Basic Framed-Slotted ALOHA (Lee et al., 2008); Dynamic
Framed-Slotted ALOHA (Ding & Liu, 2009); Enhanced Dynamic Framed-slotted ALOHA
(Lee & Lee, 2006); and Probabilistic Cluster-Based Technique (Pupunwiwat & Stantic, 2010d),
to enhance the performance efficiency of the data capturing process. In addition, several
Frame Estimation approaches have been suggested to improve the accuracy of frame-size
prediction including the Schoute method (Schoute, 1983), the Lowerbound method, the
Chen1 and Chen2 methods (Chen, 2006), the Vogt method (Vogt, 2002), the Bayesian method
(Floerkemeier, 2007), and the Precise Tag Estimation Scheme (Pupunwiwat & Stantic, 2010b),
(Pupunwiwat & Stantic, 2010a).
The deterministic method operates by asking for the first EPC string of the tag until it gets
matches for the tags, it will then continues to ask for additional characters until all tags within
the region are found. There have been several methods proposed in literature in order to
improved quality of the captured data such as: the Query Tree (Myung & Lee, 2006a); the
Adaptive Splitting Tree (Myung & Lee, 2006b); the Hybrid Query Tree (Ryu et al., 2007); and
the Joined Q-ary Tree (Pupunwiwat & Stantic, 2009), (Pupunwiwat & Stantic, 2010c).
Tan, Sheng and Li have proposed in their research the utilisation of a threshold to identify an
excessive amount of missing RFID readings (Tan et al., 2008). By using two different protocols,
the trusted reader and un-trusted reader protocols, the methodology analyses a RFID data set
and finds missing data without the need for ascertaining tag identifiers. The system will then
consult a threshold defined by the owner as to the number of missing tags which are tolerable
in a given situation with the system alerting the user if this threshold is breached. It will not
however replace the missed readings.
Statistical Approximations refer to the use of a Model-Based Querying system to return
approximate readings found from the sensor networks (Deshpande et al., 2004; Deshplande
et al., 2005). Although this method is not used primarily for RFID technology, the method is
applied to wireless sensors which provide additional functionality that RFID tags do not (i.e.
Temperature Sensors). This approach is designed to capture a query from the User, find the
values from the sensor readings, and return approximate values to the User.
5.3 Deferred approaches
We have defined Deferred Approaches as methodologies applied at a deferred stage of the
capturing cycle when the observational data is stored in the database. This includes P2P
Networks, Probabilistic Tag Proximity Detection, Cost-Conscious Cleaning, Data Mining
Techniques, Probabilistic Inference and Probabilistic Event Extraction.

The P2P Collaboration method, proposed by Peng, Ji, Luo, Wong and Tan (Peng et al., 2008),
is an approach utilising Peer-to-Peer (P2P) networks within the RFID data set to detect and
remove inaccurate readings. The system works by breaking the readings into detection nodes,
which are constantly sending and receiving messages. From these transmitted messages, false
negatives and false positives are able to be detected and corrected resulting in a cleaner data
set.
Ziekow and Ivantysynova have presented a method designed to correct RFID anomalies
probabilistically by employing maximum likelihood operations (Ziekow & Ivantysynova,
2008). Their method utilises the position of a tag which may be determined by measuring
properties associated with the Radio Frequency signal.
The Cost-Conscious cleaning method is a cleaning algorithm which utilises a Bayesian
Network to judge the likelihood that read tags correctly depict reality when based upon the
previously read tags (Gonzalez et al., 2007). The Cost-Conscious cleaning approach houses
several different cleaning algorithms and chooses the least costly algorithm which would offer
the highest precision in correcting the raw data. A similar approach has also been proposed
that utilises a Bayesian Network to judge the existence of tags scanned (Floerkemeier, 2004).
It lacks, however, the cost-saving analysis that would increase the speed of the clean.
Data Mining Techniques refer to the use of mining past data to detect inaccuracies and possible
solutions to raw RFID readings. A study which has used data mining techniques extensively
to correct the entire data set table is the Deferred Rule Based Approach proposed in (Rao et al.,
2006). The architecture of the system is reliant on the user defining rules which are utilised to
determine anomalies in the data set and, possibly, to correct them.
Probabilistic Inference refers to a process by which the in-coming data node will be evaluated.
This is primarily based upon the weight of its likelihood and the weight of the remainder of
the readings (Cocci et al., 2007; 2008). The cleaning algorithm utilises several techniques to
correct that data such as Deduplication, Time conversion, Temporal Smoothing and Anomaly
Filtering, and, additionally, uses a graph with probabilistic weights to produce further
inferences on the data.
Probabilistic High Level Event Transformations refers to the process of observing the raw
partial events of RFID data and transforming these into high level probable events. It has
been primarily used in a program entitled Probabilistic Event EXtractor (PEEX) which has
evolved from several publications. In its embryonic phase, Khoussainova, Balazinska and
Suciu published a paper detailing the use of an algorithm called StreamClean which employ
probabilistic inference to correct incoming data (Khoussainova et al., 2006).
A year after this article, the first papers for PEEX were published. This described the
method which enabled high level event extraction based upon probabilistic observations
(Khoussainova et al., 2007; Khoussainova, Balazinska & Suciu, 2008). The system architecture
deciphers the raw RFID information searching for evidence which a high level event
transpired. The system uses a Confidence Learner, History Lookup and Event Detector to
enhance the reliability of the returned events. By transferring these low level readings into
high level events, PEEX engages in cleaning as the process of probabilistically by categorising
the results of these events, and in the process, caters for missed and inaccurate readings.
Currently, PEEX is being incorporated into a new a system named Cascadia where it will be
utilised to help perform high level management of RFID tracking in a building environment
(Khoussainova, Welbourne, Balazinska, Borriello, Cole, Letchner, Li, Ré, Suciu & Walke,
2008; Welbourne et al., 2008). Bayesian Networks have also been implemented in several
studies to infer high level behaviour from the raw readings. The specific application was first
17

demonstrated on a traveller moving through an urban environment (Patterson et al., 2003)
and the second using RFID tags to track the activities of daily living (Philipose et al., 2004).
In previous work, we have proposed the concept of using high level classifiers coupled with
intelligent analysis to correct the various anomalies found in RFID data. First, we examined
the potential of employing a simple algorithm that corrects a simple missed reading (Darcy
et al., 2007). We then proposed the utilisation of highly intelligent analytical processes coupled
with a Bayesian Network (Darcy et al., 2009b;c), Neural Network (Darcy, Stantic & Sattar,
2010a) and Non-Monotonic Reasoning (Darcy et al., 2009a; Darcy, Stantic & Sattar, 2010b)
to correct missing RFID Data. Following this, we applied our Non-Monotonic Reasoning
approach to both false-negative and false-positive data anomalies (Darcy, Stantic & Sattar,
2010d). We then also introduced a concept to extract high level events from low level readings
using Non-Monotonic Reasoning (Darcy, Stantic & Sattar, 2010c). Finally, we proposed a
methodology that considers and differentiates between a false-positive anomaly and breach
in security using Non-Monotonic Reasoning (Darcy, Stantic, Mitrokotsa & Sattar, 2010).
6. Drawbacks and proposed solutions for current approaches
In this section, we highlight several drawbacks we have found associated with the various
methodologies currently employed to correct RFID captured data. We also supply our
suggested solutions to these problems where possible in an effort to encourage further interest
in this field of research. Finally, we conclude with an overall analysis of these methodologies
and their respective drawbacks.
6.1 Physical drawbacks and solutions
With regard to Physical Approaches, we have highlighted three main drawbacks and our
suggested solutions to correct these issues where possible:
• Problem: The main problem that we foresee with the utilisation of Physical Approaches is
that it usually only increases the likelihood that the missed objects will be found.
Solution: We do not have a solution to the problem of physically correcting wrong
or duplicate anomalies other than suggesting to utilise Middleware and/or Deferred
solutions.
• Problem: Physical Approaches generates artificial duplicate anomalies in the event that all
the tags attached are read.
Solution: Specific software tailored to the application to automatically account for the
artificially generated duplicate anomalies could be used for correction filtering at the edge.
• Problem: Physical Approaches suffer from additional cost to the user or more labour to
purchase extra tags, equipment or time to move the objects.
Solution: We do not believe there is a solution to this as Physical Approaches demand
additional labour for the user to correct the mistakes as opposed to Middleware or
Deferred Approaches.
6.2 Middleware drawbacks and solutions
We found three major drawbacks to the Middleware Approaches that prevent these from
acquiring their maximum integrity. These issues include:
• Problem: Correcting incoming data at the edge of the RFID capture process will not
provide the cleaning algorithm with adequate information needed to deal with highly

ambiguous and complex anomalies.
Solution: We believe that to correct this drawback, the user must employ a Deferred
methodology in addition to the Middleware Approach to utilise all stored readings. This
would result in more observational data eliminating highly ambiguous anomalies.
• Problem: When utilising probabilistic algorithms such as Bayesian Networks to correct
anomalies, there is a risk of the methodology introducing artificially generated anomalies.
This may occur in cases such as the training set not reflecting the reality of the scenarios or
the system probabilistically choosing the incorrect action to take in a situation.
Solution: To correct this issue, the user may be able combine various probabilistic
techniques together or to employ a deterministic approach in order to enhance the method
of cleaning the database.
• Problem: RFID data streams that are captured by readers can be accumulated quickly
resulting in data collisions. Simultaneous transmissions in RFID systems will also lead
to collisions as the readers and tags typically operate on the same channel. There are
three types of collisions possible to occur: Reader-Tag collision, Tag-Tag collision, and
Reader-Reader collision.
Solution: It is crucial that the RFID system must employ anti-collision protocols in readers
in order to enhance the integrity of the captured data. However, the step of choosing
the right anti-collision protocol is also very important, since we cannot depend solely on
the capability of anti-collision protocol itself, but also on the suitability of each selected
technique for the specific scenario. The user may employ decision making techniques such
as both the Novel Decision Tree and the Six Thinking Hats strategy for complex selective
technique management to determine the optimal anti-collision protocol. The novelty of
using complex selective technique management is that we will get the optimal outcome
of anti-collision method for the specific scenario. This will, in turn, improve the quality of
the data collection. It will also help over long period of use when these captured data are
needed for transformation, aggregation, and event processing.
6.3 Deferred drawbacks and solutions
While reviewing the Deferred Approaches to correct RFID anomalies, we have discovered
that there are certain shortcomings when attempting to clean captured observational data.
• Problem: Similar to the Middleware Approaches which utilise probabilistic calculations,
a major problem in the Deferred Approaches is that due to the nature of probability, false
positive and negatives may be unintentionally introduced during cleaning.
Solution: As stated previously, the inclusion of multiple probabilistic techniques or even
deterministic approaches should increase the intelligence of the methodology to block
artificial anomalies from being generated.
• Problem: Specifically with regard to the Data Mining technique, it relies on the order the
rules appear as opposed to using any intelligence to decipher the correct course of action.
Solution: It is necessary to increase the intelligence of the order of the rule order by
integrating high level probabilistic or deterministic priority systems.
• Problem: With regard to the Cost-Conscious Cleaning method, due to the fact that the
method only utilises immediate previous readings and focuses on finding the least costly
algorithm, accuracy may be lowered to ensure the most cost-effective action.
Solution: In the event that this algorithm is applied at a Deferred stage, it will not require
19

the data to be corrected as fast as possible. Therefore in this situation, the emphasis on
cost-effectiveness is not relevant as is usually the case and other actions could be examined
to derive the highest accuracy.
• Problem: As a general constraint of all Deferred Approaches, it is necessary to apply the
correction algorithm at the end of the capture cycle when the data is stored in the Database.
The main problem with this characteristic is that the methodologies will never be able to
be applied as the data is being captured and, therefore, cannot correct in real-time.
Solution: As most of the Deferred Approaches, especially the Data Mining and Highly
Intelligent Classifier, requires certain observational data to correct anomalies, we propose
the use of a buffering system that runs as the data is being captured and takes snapshots
of the read data to correct any anomalies present. Unfortunately, due to the need that the
methodology is run in real-time, it may not be able to include all the complexities of the
current Deferred Approaches such as dynamic training of the classifiers.
6.4 Drawback analysis
In this research, we evaluated the current state-of-the-art approaches designed to correct the
various anomalies and issues associated with RFID technology. From our findings, we have
found that, while Physical Approaches do increase the chances of a tag being captured, it does
generate duplicate anomalies and places cost in both time and labour onto the user that may
not be beneficial. With regard to Middleware Approaches, we found that most anomalies
are corrected through these techniques. However, due to the limited scope of information
available, the more complex procedures such as dealing with highly ambiguous errors or
transforming the raw observations into high-level events is not possible. In contrast, Deferred
Approaches have an advantage to correct highly ambiguous anomalies and transform events.
Its main issue, however, is not being available to process the observational information in
real-time limiting its cleaning to a period after the records have been stored.
Overall, we have found from our research that a truly robust RFID system that eliminates
all possible natural and artificial anomalies generated will require the integration of most
approaches we have recognised. For example, various real-time anomalies are best filtered at
the edge while increasingly ambiguous anomalies can only be corrected at a deferred stage of
the capture cycle. Additionally, we found that there is a need to, not only employ probabilistic
techniques, but also deterministic where possible as it theoretically should reduce the artificial
anomalies produced. We, therefore, recommend the inclusion of all methods where possible,
at least one of the Middleware and Deferred categories, and, where applicable, the inclusion
of both deterministic and probabilistic techniques.
7. Conclusion
In this study, we have examined RFID technology and its current uses in various applications.
We have also examined the three various issues among the integration of the systems
including security, privacy and data abnormalities. Furthermore, we have examined the
data abnormality issue to find that four problems exist including low-level nature, large
intakes, data anomalies and complex spatial and temporal aspects. There have been various
methodologies proposed in the past to address the various problems in the data abnormalities
categorised into physical, middleware and deferred solutions. Unfortunately, due the various
drawbacks such as application-specified solutions, lack of analytical information or reliance

on user-specified/probabilistic algorithms, current approaches do not provide the adequate
support needed in RFID systems to be adopted in commercial sectors.
Specifically, we contributed the following to the field of RFID study:
• We provided a detailed survey of RFID technology including how it was developed,
its various components and the advantages of integrating its technology into business
operations.
• We highlighted the current usages of RFID categorising it into either “Integrated RFID
Applications” and “Specific RFID Applications”.
• We examined the various issues preventing the adoption of RFID technology including the
concerns of security, privacy and characteristics. We also focused on the specific Anomalies
generated by the capturing hardware including wrong, duplicate and missing errors.
• After examining the issues surrounding RFID, we investigated the state-of-the-art
approaches currently employed for correction. We categorised these methodologies into
Physical, Middleware or Deferred Approaches.
• Finally, we explored the drawbacks found in currently employed Approaches and
suggested several solutions in the hope of generating interest in this field of study.
With regard to future work, we specifically would like to extend our previous studies
discussed in Section 5.3 by allowing it to function in real-time. We would do this through
the creation of a buffer system discussed in Section 6.3 by taking snapshots of incoming data
and correcting anomalies where found. We also firmly believe that this sincerely is the next
step of evolution of our approach to allow it to be employed as the observational records are
read into the Middleware.
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2
RFID Components, Applications and System
Integration with Healthcare Perspective
Kamran Ahsan
Staffordshire University
UK
1. Introduction
RFID (radio frequency identification) technology has already proved its use in various areas
such as security, library, airline, military, animal forms, sports and other areas. RFID is
being used for various applications in many industries. For example, equipment tracking,
access controls including personal and vehicle, logistic, baggage, items security in
departmental store. The main advantages RFID provide is resource optimization, quality
customers’ care, enhanced accuracy, efficient business processes, and effective business and
healthcare processes. RFID can help is recognizing contextual knowledge and can help to
improve objects predictability for certain processes. However, it is necessary to study RFID
components for using these in healthcare environment. RFID main components are
antennas, tags and readers. The investigation of these components provides an
understanding of its use in healthcare settings and integration in healthcare processes.
This chapter studies the RFID components such as Antenna and reader. This chapter
discusses the RFID active and passive tags, and compare these tags including advantages
and disadvantages of RFID system. In this chapter, RFID applications are explored and
technical model is analyzed. It also considers the healthcare perspectives and RFID use
within healthcare settings. This study constructs a model for connected RFID applications
which provides quick support for various healthcare functions and enhances flexibility for
various systems’ components integration.
2. Motivation of RFID technology
Existing research suggests that healthcare organisations are adopting information
technology, specifically mobile technology throughout the world including the USA, Europe
and UK (Bharadwaj et al., 2001). In the UK, the NHS (NHS-UK, 2009) is keen to adapt
mobile technology for better information handling and this argument is supported in this
chapter. However, real-time techniques and contextual knowledge management concepts
for instant care is somehow neglected (Watson, 2006). Healthcare processes are volatile and
the context of information changes rapidly. New technology has not considered information
within their context. The context of information is more complex in healthcare in
comparison to other industries. Although businesses have already started to develop and
implement mobile technology for handling contextual information to improve processes but
the same approaches cannot be adopted in the healthcare industry due to dominant

28
knowledge use rather than just information and substantial human involvement
(Connecting for health, 2009). However, the proven technology in business scenarios such as
RFID can be adopted for a healthcare situation with the appropriate modelling of its use.
Managing context for any information is a difficult task but information systems play an
important role into it but contextual knowledge is even more difficult and need location, time
and duration for information for providing context to any knowledge (Bharadwaj et al., 2001).
If knowledge gets support with context of objects’ location, duration and time then this
contextual knowledge can improve various situations for resource optimization and instant
better actions. RFID technology use is critical to get this knowledge and providing context to
it. RFID can also support tacit knowledge on a real-time basis in healthcare situations such
as patients moving between locations to get medical treatment and a change in their medical
condition at the same time. The utilization of tacit knowledge is crucial but it needs context
environmental knowledge for instance actions. One of the properties of RFID is to provide
instant location information of any object associated to it and this can play a vital role for
tacit knowledge support and managing other environmental knowledge. Advanced use of
RFID technology can integrate patients’ flow processes appropriately and support patients’
treatment processes by deterministic patients’ movement knowledge (location and time etc.)
within hospital settings (Connecting for health, 2010).
In a healthcare situation the patients’ movement processes are subject to change due to
various reasons including a change in the patients’ medical condition, due to the
unavailability of a particular resource at any given time and the unpredictable duration of
any medical procedure (DH-UK, 2009). When processes are executed according to a plan
and schedule then it consumes healthcare resources in a predicted way, if processes change
due to any of the reasons described above then time and resources may be misused or
processes become unpredictable. These situations consume resources unnecessarily and the
instability of one process at one location may affect other processes at another location. So,
the use of RFID technology is crucial for determining situations through getting time and
location of an object within healthcare settings. Use of RFID technology is important for
better process management including improved decision-making.
3. RFID utilisation
RFID works for identification of items/objects (Bohn, 2008). Sometime it only identifies item
category or type but it is capable of identify items/objects uniquely. RFID also enables data
storage for remote items/objects through remotely access items information (Schwieren1 &
Vossen, 2009). RFID system consists of RFID tags, RF Antennas, RFID readers and back-end
database for storing unique item’s ID. In RFID systems, RFID tags use as unique identifier,
these tags associate with any items, when system reads these unique tags then information
associated with that tags can be retrieved. Antennas are first point of contact for tags
reading. Reader can only work with software resides in reader’s ROM (Glover & Bhatt,
2006). RFID system is based upon tags and reader’s communication and range of
communication/reading depends on operating frequency. When antennas deduct tags then
an application which is part of reader manipulates tags’ information in readable format for
the end user. There is a great amount of research being conducted to improve the efficiency
of RFID systems, increasing the accuracy of RFID reader and the feasibility of RFID tags.
Although RFID accuracy needs more enhancement and efficiency yet to be increase but still
RFID system is used in many applications (Bohn, 2008). There are a variety of tags, readers

RFID Components, Applications and System Integration with Healthcare Perspective 29
and antennas types are available. Before implementing RFID system, selection among these
types needs understanding of these types in relation to their feasibility, capabilities and
reliability. It is also necessary to understand combinational use of these types for
implementing a single feasible RFID system.
4. Research approach
Qualitative research methodology is followed for observing the patients’ flow situation
within hospital settings. It includes observation and open interviews. This study tries to find
out the pattern within hospital condition, knowledge elements for healthcare processes and
priority of each knowledge element for knowledge factor integration with the help of
location deduction technology (RFID). Some individual scenarios are considered within
patients’ movement processes and understanding is build for integration of RFID
integration within these processes. In this respect, qualitative methodology is sufficient for
including each knowledge element and device a way of handling these elements through
location deduction technology. This chapter explores RFID technology with its kinds, types
and capabilities. It is conferred that how RFID technology can be generalised through
generalise technical model. It is discussed that how component layering approach can be
feasible for integrating various healthcare management disciples for providing improved
management. Healthcare knowledge factors are considered for supporting knowledge
elements through RFID technology to improve healthcare situation.
5. RFID evaluation
RFID technology continues to evolve in past years in terms of various shapes of tags for
increase its feasibility of its use, fast reading rate of reader and range of antennas etc. The
use of RFID also evolves due to enhancement in its components. As the accuracy increases,
the use of technology also increases such as baggage handling, goods delivery tracking and
courier services. RFID system enhancement also evolves automation applications
development e.g. automatic toll payments, automatic equipment tracking and document
management etc. (Garfinkel & Rosenberg, 2005). In this connection, the evolution process of
RFID with respect to past few decades can be seen in figure 1.
6. How RFID system works
The basic unit of RFID system is tags and tags have its own unique identification number
system by which it recognizes uniquely. These unique identification numbers save in tags’
internal memory and it is not changeable (read-only). However, tags can have other
memory which can be either read-only or rewrite able (Application Notes CAENRFID,
2008). Tag memory may also contain other read-only information about that tag such
manufactured date. RFID reader generates magnetic fields through antennas for getting
acknowledgement from tags (Garfinkel & Rosenberg, 2005). The reader generates query
(trigger) through electromagnetic high-frequency signals (this frequency could be up to 50
times/second) to establish communication for tags (Srivastava, 2005). This signal field might
get large number of tags data which is a significant problem for handling bulk of data
together. However, this problem can be overcome through filtering these data. Actually
software performs this filtering and information system is used to supply this data to data

30
Fig. 1. RFID evolution: over past the few decades (Srivastava, 2005)
repository or use any other software procedures to control data according to the need and
system capability (Srivastava, 2005; Application Notes CAENRFID, 2008). This piece of
software works as a middle layer between user application and reader because the reader
normally does not have the capability to handle bulk data at once; it has the job to supply
reading data to user application for further process (Frank et al., 2006). This buffering
capability may supply data from reader to information system interface (user interface)
directly or may provide and use some routine to save into database for later exploit, it is
depend on user requirement.
Reader and tags communication can be maintained through several protocols. When the
reader is switched on then these protocols start the identification process for reading the
tags, these important protocols are ISO 15693, ISO 18000-3, ISO 18000-6 and EPC. ISO 15693
and ISO 18000-3 protocols are used for high frequency (HF) and, ISO 18000-6 and EPC
protocols are used for ultra high frequency (UHF). Frequency bands have been defined for

these protocols and they work within specified range such as HF has 13.56 MHz and UHF
between 860 – 915 MHz (Application Notes CAENRFID, 2008). Reader modulates tags
responses within frequency field (Parks et al., 2009).
The reader handles multiple tags reading at once through signal collision detection
technique (Srivastava, 2005). This signal collision detection technique uses anti-collision
algorithm, the use of this algorithm enables multiple tag handling. However, multiple tags
handling depend on frequency range and protocol use in conjunction with tag type which
can enable up to 200 tags reading at single time. Reader protocol is not only use for reading
the tag but also perform writing on to tags (Application Notes CAENRFID, 2008).
Fig. 2. A typical RFID system (Application Notes CAENRFID, 2008)
The use of the reader within RFIFD system can be seen in figure 2. This figure also define
the overall cycle of tag reading by reader through antenna and transforming data into
communicate able form to user applications.
7. How RFID system works
RFID system deducts tags within antennas’ range and performs various operations onto
each tag. The RFID system can only work effectively if all RFID components logically
connect together and these components need to be compatible with each other. Thats’ why
understanding of these separate components is necessary. Implementation of complete RFID
solution is only possible through integration of these components which needs
understanding of compatibility for each component, realisation of each components
compatibility needs property study for these components (Sandip, 2005). These components
are gathered and defined as under. Also integration of these components can be understood
with figure 3.

32
• Tag has unique ID and use for unique identification; tags are attached with objects in
RFID solutions.
• Antenna use for reading tags; antenna has its own magnetic field and antenna can only
read tags within these magnetic fields.
• Reader works for handling antenna signals and manipulate tags’ information.
• Communication infrastructure use for reader to communicate with IT infrastructure
and work as middle layer between application software and reader.
• Application software is a computer base software which enable user to see RFID
information, this can be database, application routines or user interface.
Fig. 3. Components of an RFID system
8. RFID tags
RFID tag has memory in the form of a microchip which store unique code for tag’s
identification, this unique identification called tag’s ID (Application Notes CAENRFID,
2008). The microchip is a small silicon chip with embedded circuit. Numbering technique is
used for providing unique identification (Garfinkel & Rosenberg, 2005). This microchip
could have read-only or writeable characteristics depending on tag type and its application
within RFID solution. These characteristics depend on the microchip circuitry which has
form and initialize during tag manufacturing (Miller & Bureau, 2009). Some tags (read-only)
re-programming is possible but need separate electronic equipment for re-programming
read-only tag’s memory. Writable tags also know as re-write tags do not need any separate
equipment and reader can write data on it, depend on the protocol support, if reader have
writing command capability and tags are in range. Tags selection is very important for
feasible use in RFID solution. This selection is dependent on the tag size, shape and material.
Tags can be integrated in varity of material depending on the need of the environment. The
tag is embedded in plastic label in form of a microchip, stick able material for documents
handling, plastic material with use of pin for use in cloths material are the good examples to
be consider (Frank et al., 2006). Various forms of tags with respect to its sizes and shapes can
understand with figure 4.

Fig. 4. Varity of RFID tags (various shape & sizes) (Frank et al., 2006)
Classification of RFID tags is also possible with respect to their capabilities such as read-
only, re-write and further data recoding. Further data recording examples are temperature,
motion and pressure etc. (Narayanan et al., 2005). Compiled tags classification into five
classes previously gathered by Narayanan et al. (2005) is shown in figure 5.
Fig. 5. RFID tags classifications (Narayanan et al., 2005)
Active, semi-active and passive are the three main tags types. Tags made up with few
characteristics which may vary slightly depending on type of tag, due to which their use can
be change in RFID solution (Zeisel & Sabella, 2006). So, selection of tags depends on the

34
functional need of RFID application. The main difference is between active and passive tags
because semi-active tags have mix of both tag’s characteristics (Application Notes
CAENRFID, 2008). These types differentiate upon memory, range, security, types of data it
can record, frequency and other characteristics. The combinations of these characteristics
effects tags’ performance and change its support and usefulness for RFID system (Intermec,
2009). The main tag types (active and passive tags) are compared in following figure 6.
Fig. 6. RFID active and passive tags comparison
8.1 Tags physical features
The tags have various physical features such as shape, size and weight. Consideration of
these features depends on environment tag being used. Classified tag’s physical features are
as under.
• Smart labels can embed in layers type materials such as papers.
• Small tags can embed objects other then flat panel such as clothes and keys.
• Plastic disks can use for attaching with durable objects and use in tough environments
such as pallets tagging use in open air.
8.2 Tags capabilities
The tags can also be differentiated with respect to tags capabilities and performance
(Schwieren1 & Vossen, 2009; Garfinkel & Rosenberg, 2005). Following is the list for tags
capabilities.

• Anti-collision capability of a tag, tags having anti-collision can enable reader to
recognize its beginning and ending which help reader to read all tags in its range.
• How tags get its power source such as active has its own battery and passive get power
from reader through its magnetic field.
• Conditions of tag environment such as use in water.
• Tags data writing capabilities such as write one time or many times onto tag memory.
• Coupling mechanism tag use such as magnetic, inductive, capacitive and backscatter.
Coupling mechanism determines tags information and power sharing methods.
• If tag can work for more than one protocol which enable tags to work with different
types of readers.
• Tags with encrypted data handling feature.
• Either tag has two way communication (full duplex) or one way communication (half
duplex).
8.3 Tags standards
Understanding of tags standards is necessary for working with various systems, protocols
and procedures. It is dependent on organisational policies and scope of RFID system. Tags
standards enable interoperability capability to RFID solutions (Sandip, 2005). For example, if
tags have standardization and its uniqueness can be identified across different systems then
it enhances the use of standard tags (Schwieren1 & Vossen, 2009). The spectrum of tags can
be single situation such as tags use in single warehouse, multiple spectrums such as same
tags use in logistic and supply chain and need recognition across different organisations and
various systems (Shepard, 2005). The selection of tags standards within RFID solutions
depend on these spectrum. Following three standards are gathered by (Shepard, 2005).
ISO/IEC 18000 tags: This standard works for various frequency ranges including long range
(UHF), high frequency (HF), low frequency (LF), and microwave. This standard supports
various principle and tags architectures. The range of tag identification includes 18000-(1 to 7).
ISO 15693: In this standard tag IDs are not as unique as ISO 18000. Although vendors try to
build unique tags with certain specification and coding but it is not globally unique. These
standard tags most often use in smart cards for contact-less mechanism. However, it is also use
in other application but in local scenario (not global) e.g. supply chain and asset tracking etc.
EPC tags: It is the standard for maintaining the uniqueness under certain management
bodies. It carries out tags uniqueness with all the vendors associated with one management
entity. Management entities carry their own EPC number technique and own the certain
object class.
8.4 Tags states
Tags process recognize with its state within RFID working environment. Tags cannot have
multiple states simultaneously. The set of tag states depend on the type of tag. However,
these states generally include open state, reply state, ready state, acknowledge state,
arbitrate state, killed state and secured state (Shepard, 2005).
8.5 Tags frequencies and range
RFID tags capability and working feasibility change according to its frequency and range.
Tags prices and its use also vary in relation with tags frequency and range. Various
frequencies and its range (working distance) can be seen in following figure 7.

36
Fig. 7. RFID frequencies and ranges
The performance, range and interference feasibility depend on the frequency at which tags’
operate (Zeisel & Sabella, 2006). Different tags standard uses different frequency bands in
which ISO and EPCglobal standard are major organisations working for UHF bands for
developing international standards (Narayanan et al., 2005). However, full compatibility is
still not achieved that’s why most of the organisation obligated to use International
Telecommunication Union principles (DHS, 2006). These principles include following
frequency bands.
• High frequency can work up to one meter. It can embed with thin objects such as
papers, that’s why it is mostly use in sales points and for access controls. 13.56MHz is
the frequency at which it work and it is less expensive to implement (Srivastava, 2005;
Application Notes CAENRFID, 2008).
• Low frequency fulfils short range applications’ needs. It is not effective for metal or wet
surfaces and only works half of the high frequency range (maximum half a meter) (Frank
et al., 2006). Low frequency works on 125 KHz (Application Notes CAENRFID, 2008).
• Ultra high frequency has better read rate and large number of UHF tags can be
recognize at one time. It has also good better read range and three times with high
frequency, it is capable to read tags up to three meters. However, range can be reduced
in wet environment. It works between 860-930 MHz frequencies (Srivastava, 2005).
• Microwave has less read range and it works within one meter. But it has rate of reading
is faster than UHF with very little affect on wet and metal surfaces. It works on Giga
Hertz frequency and faster than LF, HF and UHF, that’s why it can work better for
vehicle access application (Application Notes CAENRFID, 2008).
8.6 Tags fields
Active tags have its own power but passive tags get the power from antenna based on
readers’ signal to antenna (Application Notes CAENRFID, 2008). Passive tags response or
communication signal is based on the power it gets from antenna. Following two methods
passive tags use for getting power from reader.

Another Random Scribd Document
with Unrelated Content

from oblivion by Dr. Stewart, rather than with the longer and
commonly corrupted version still to be heard by the croft-fire in
many localities, all "the far cry" from the Ord of Sutherland to the
Rhinns of Islay. The "Laoidh Mhnathan"—the Chant of Women, at p.
100—is not ancient in the actual form here given, which is from an
unpublished volume of "Oràin' Spioradail."
The sweetest-voiced of the younger Irish singers of to-day has
spoken of the Celtic Twilight. A twilight it is; but, if night follow
gloaming, so also does dawn succeed night. Meanwhile, twilight
voices are sweet, if faint and far, and linger lovingly in the ear.
There is another Pàras than that seen of Alastair of Innisròn—the
Tir-Nan-Oigh of friendship. Therein we both have seen beautiful
visions and dreamed dreams. Take, then, out of my heart, this book
of vision and dream.
Fiona Macleod.
"O bileag-geal,
O bileag-na-Toscùil, bileag Pharais,
O tha e boidheach!
Tha e boidheach!"

I
It was midway in the seventh month of her great joy that the child
moved, while a rapture leaped to her heart, within the womb of
Lora, daughter of the dead Norman Maclean, minister of Innisròn, in
the Outer Isles.
On the same eve the cruel sorrow came to her that had lain waiting
in the dark place beyond the sunrise.
Alastair, her so dearly beloved, had gone, three days earlier, by the
Western Isles steamer, to the port of Greenock, thence to fare to
Glasgow, to learn from a great professor of medicine concerning that
which so troubled him—both by reason of what the islesmen
whispered among themselves, and for what he felt of his own secret
pain and apprehension.
There was a rocky spur on Innisròn, whence the watcher could scan
the headland round which the Clansman would come on her thrice-
weekly voyage: in summer, while the isles were still steeped in the
yellow shine; in autumn, when the sky seaward was purple, and
every boulder in each islet was as transparent amber amid a vapour
of amethyst rising from bases and hollow caverns of a cold day-
dawn blue.
Hither Lora had come in the wane of the afternoon. The airs were as
gentle and of as sweet balmy breath as though it were Summer-
sleep rather than only the extreme of May. The girl looked, shading
her eyes, seaward; and saw the blue of the midmost sky laid as a
benediction upon the face of the deep, but paler by a little, as the
darkest turquoise is pale beside the lightest sapphire. She lifted her

eyes from the pearl-blue of the horizon to the heart of the zenith,
and saw there the soul of Ocean gloriously arisen. Beneath the
weedy slabs of rock whereon she stood, the green of the sea-moss
lent a yellow gleam to the slow-waving dead-man's-hair which the
tide laved to and fro sleepily, as though the bewitched cattle of
Seumas the seer were drowsing there unseen, known only of their
waving tails, swinging silently as the bulls dreamed of the hill-
pastures they should see no more. Yellow-green in the sunlit spaces
as the sea-hair was, it was dark against the shifting green light of
the water under the rocks, and till so far out as the moving blue
encroached.
To Lora's right ran a curved inlet, ending in a pool fringed with
dappled fronds of sea-fern, mare's-tails, and intricate bladder-wrack.
In the clear hollow were visible the wave-worn stones at the bottom,
many crowned with spreading anemones, with here and there a
star-fish motionlessly agleam, or a cloud of vanishing shrimps above
the patches of sand, or hermit crabs toiling cumbrously from perilous
shelter to more sure havens. Looking down she saw herself, as
though her wraith had suddenly crept therein and was waiting to
whisper that which, once uttered and once heard, would mean
disunion no more.
Slipping softly to her knees, she crouched over the pool. Long and
dreamily she gazed into its depths. What was this phantasm, she
wondered, that lay there in the green-gloom as though awaiting
her? Was it, in truth, the real Lora, and she but the wraith?
How strangely expressionless was that pale face, looking upward
with so straightforward a mien, yet with so stealthy an
understanding, with dark abysmal eyes filled with secrecy and dread,
if not, indeed, with something of menace.
A thrill of fear went to the girl's heart. A mass of shadow had
suddenly obscured her image in the water. Her swift fancy suggested
that her wraith had abruptly shrouded herself, fearful of revelation.

The next moment she realised that her own wealth of dark hair had
fallen down her neck and upon her shoulders—hair dusky as twilight,
but interwrought with threads of bronze that, in the shine of fire or
sun, made an evasive golden gleam.
She shuddered as she perceived the eyes of her other self intently
watching her through that cloudy shadow. A breath came from the
pool, salt and shrewd, and cold as though arisen from those sea-
sepulchres whence the fish steal their scales of gold and silver. A
thin voice was in her ears that was not the lap of the tide or the
cluck of water gurgling in and out of holes and crannies.
With a startled gesture she shrank back.
"What is it? What is it?" she cried; but the sound of her own awed
voice broke the spell: and almost at the same moment an eddy of
wind came circling over the rock-bastions of the isle, and, passing as
a tremulous hand over the pool, ruffled it into a sudden silvery
sheen.
With a blithe laugh, Lora rose to her feet. The sunlight dwelt about
her as though she were the sweetest flower in that lost garden of
Aodh the poet, where the streams are unspanned rainbows flowing
to the skyey cauldrons below the four quarters, and where every
white flower has at dusk a voice, a whisper, of surpassing
sweetness.
"O Alastair, Alastair!" she cried, "will the boat never be coming that
is to bring you back to me!"
Not a black spot anywhere, of wherry or steamer, caught the leaping
gaze. Like a bird it moved across the sea, and found no object
whereon to alight.
The Clansman was often late; but her smoke could be seen across
Dunmore Head nigh upon quarter of an hour before her prow
combed the froth from the Sound.

With a sigh, the girl moved slowly back by the way she had come.
Over and over, as she went, she sang, crooningly, lines from a sweet
song of the Gael, O, Till, a Leannain!
As she passed a place of birchen undergrowth and tall bracken, she
did not see an old man, seated, grey and motionless as a heron. He
looked at her with the dull eyes of age, though there was pity in
them and something of a bewildered awe.
"Ay," he muttered below his breath, "though ye sing for your dear
one to return, ye know not what I know. Have I not had the vision
of him with the mist growin' up an' up, an' seen the green grass turn
to black mools at his feet?"
Lora, unwitting, passed; and he heard her voice wax and wane, as
falling water in a glen where the baffled wind among the trees
soughs now this way and now that:—
"Mo chridhe-sa! 's tusa 'bhios truagh, 'bhios truagh,
Mur pill is' 'thog oirre gu cluaidh, gu cluaidh!"
She went past the boulder on the path that hid the clachan from
view, and within a net-throw of which was the byre of Mrs.
Maclean's cottage, where, since her father's death, she had dwelt.
A tall, gaunt, elderly woman, with hair of the ivory white of the
snowberry, was about to pass from behind the byre with a burthen
of fresh bracken for Ian Maclean's bed—for the old islesman abode
by the way of his fathers, and was content to sleep on a deerskin
spread upon fresh-gathered fern—when she caught sight of Lora.
She stopped, and with an eager glance looked at the girl: then
beyond, and finally seaward, with her long, thin, brown arm at an
angle, and her hand curved over her eyes against the glare of the
water.
Silence was about her as a garment. Every motion of her, even,
suggested a deep calm. Mrs. Maclean spoke seldom, and when she

said aught it was in a low voice, sweet and serene, but as though it
came from a distance and in the twilight. She was of the shadow, as
the islesmen say; and strangers thought her to be austere in look
and manner, though that was only because she gazed long before
she replied to one foreign to her and her life: having the Gaelic, too,
so much more natively than the English, that oftentimes she had to
translate the one speech into the other nearer to her: that, and also
because the quiet of the sea was upon her, as often with hill-folk
there is a hushed voice and mien.
Lora knew what was in her mind when she saw her gaze go seaward
and then sweep hither and thither like a hawk ere it settles.
"The boat is not yet in sight, Mary; she is late," she said simply:
adding immediately, "I have come back to go up Cnoc-an-Iolair;
from there I'll see the smoke of the Clansman sooner. She is often as
late as this."
Mrs. Maclean looked compassionately at the girl.
"Mayhap the Clansman will not be coming this way at all to-night,
Lora. She may be going by Kyle-na-Sith."
A flush came into Lora's face. Her eyes darkened, as a tarn under
rain.
"And for why should she not be sailing this way to-night, when
Alastair is coming home, and is to be here before sundown?"
"He may have been unable to leave. If he does not come to-day, he
will doubtless be here to-morrow."
"To-morrow! O Mary, Mary, have you ever loved, that you can speak
like that? Think what Alastair went away for! Surely you do not know
how the pain is at my heart?"

"Truly, mùirnean. But it is not well to be sure of that which may
easily happen otherwise."
"To-morrow, indeed! Why, Mary, if the Clansman does not come by
this evening, and has gone as you say by Kyle-na-Sith, she will not
be here again till the day after to-morrow!"
"Alastair could come by the other way, by the Inverary boat, and
thence by the herring-steamer from Dunmore, after he had reached
it from Uan Point or by way of Craig-Sionnach."
"That may be, of course; but I think not. I cannot believe the boat
will not be here to-night."
Both stood motionless, with their hands shading their eyes, and
looking across the wide Sound, where the tide bubbled and foamed
against the slight easterly wind-drift. The late sunlight fell full upon
them, working its miracle of gold here and there, and making the
skin like a flower. The outline of each figure stood out darkly clear as
against a screen of amber.
For a time neither spoke. At last, with a faint sigh, Mrs. Maclean
turned.
"Did you see Ian on your way, Lora-mo-ghràidh?"
"No."
"Do not have speech with the old man to-night, dear one. He is not
himself."
"Has he had the sight again?"
"Ay, Lora."
Again a silence fell. The girl stood moodily, with her eyes on the
ground: the elder watched her with a steadfast, questioning look.

"Mary!"
Mrs. Maclean made no reply, but her eyes brought Lora's there with
the answer that was in them.
"Ian has never had the sight again upon ... upon Alastair, has he?"
"How can I say?"
"But do you know if he has? If you do not tell me, I will ask him."
"I asked him that only yester-morning. He shook his head."
"Do you believe he can foresee all that is to happen?"
"No. Those who have the vision do not read all that is in the future.
Only God knows. They can see the thing of peril, ay, and the evil of
accident, and even Death—and what is more, the nearness and
sometimes the way of it. But no man sees more than this—unless,
indeed, he has been to Tir-na-h'Oigh."
Mrs. Maclean spoke the last words almost in a whisper, and as
though she said them in a dream.
"Unless he has been to Tir-na-h'Oigh, Mary?"
"So it is said. Our people believe that the Land of Eternal Youth lies
far yonder across the sea; but Aodh, the poet, is right when he tells
us that that land is lapped by no green waves such as we know
here, and that those who go thither do so in sleep, or in vision, or
when God has filled with dusk the house of the brain."
"And when a man has been to Tir-na-h'Oigh in sleep, or in dream, or
in mind-dark, does he see there what shall soon happen here?"
"It is said."
"Has Ian been beyond the West?"

"No."
"Then what he sees when he has the sight upon him is not
beannaichte: is not a thing out of heaven?"
"I cannot say. I think not."
"Mary, is it the truth you are now telling me?"
A troubled expression came into the woman's face, but she did not
answer.
"And is it the truth, Mary, that Ian has not had the sight upon
Alastair since he went away—that he did not have it last night or this
morning?"
Lora leaned forward in her anxiety. She saw that in her companion's
eyes which gave her the fear. But the next moment Mrs. Maclean
smiled.
"I too have the sight, Lora-mo-ghràidh; and shall I be telling you
that which it will be giving you joy to hear?"
"Ay, surely, Mary!"
"Then I think you will soon be in the arms of him you love"—and,
with a low laugh, she pointed across the sea to where a film of blue-
grey smoke rose over the ridge of Dunmore headland.
"Ah, the Clansman!" cried Lora, with a gasp of joy: and the next
moment she was moving down the path again toward the little
promontory.
The wind had risen slightly. The splash, splash, of the sunny green
waves against each other, the lapping of the blue water upon the
ledges to the east, the stealthy whisper where the emerald-green
tide-flow slipped under the hollowed sandstone, the spurtle of the

sea-wrack, the flashing fall and foam-send of the gannets, the cries
of the gulls, the slap of wind as it came over the forehead of the isle
and struck the sea a score of fathoms outward—all gave her a sense
of happiness. The world seemed suddenly to have grown young. The
exultant Celtic joy stood over against the brooding Celtic shadow,
and believed the lances of the sunlight could keep at bay all the
battalions of gloom.
The breeze was variable, for the weft of blue smoke which suddenly
curled round the bend of Dunmore had its tresses blown seaward,
though where Lora stood the wind came from the west, and even
caused a white foam along the hither marge of the promontory.
With eager eyes she watched the vessel round the point. After all, it
was just possible she might not be the Clansman.
But the last sunglow shone full against Dunmore and upon the bows
of the steamer as she swung to the helm; and the moment the red
funnel changed from a dusky russet into a flame of red, Lora's new
anxiety was assuaged. She knew every line of the boat, and already
she felt Alastair's kisses on her lips. The usual long summer-
gloaming darkened swiftly; for faint films of coming change were
being woven across the span of the sky from mainland oceanward.
Even as the watcher on Innisròn stood, leaning forward in her eager
outlook, she saw the extreme of the light lift upward as though it
were the indrawn shaft of a fan. The contours of the steamer grew
confused: a velvety duskiness overspread Dunmore foreland.
The sky overhead had become a vast lift of perishing yellow—a
spent wave of daffodil by the north and by the south; westward, of
lemon, deepening into a luminous orange glow shot with gold and
crimson, and rising as an exhalation from hollow cloud-sepulchres of
amethyst, straits of scarlet, and immeasurable spaces of dove-grey
filled with shallows of the most pale sea-green.

Lora stood as though wrought in marble. She had seen that which
made the blood leap from her heart, and surge in her ears, and
clamour against her brain.
No pennon flew at the peak of the steamer's foremast. This meant
there was neither passenger nor freight to be landed at Innisròn, so
that there was no need for the ferry.
She could scarcely believe it possible that the Clansman could come,
after all, and yet not bring Alastair back to her. It seemed absurd:
some ill-timed by-play; nay, a wanton cruelty. There must be some
mistake, she thought, as she peered hungrily into the sea-dusk.
Surely the steamer was heading too much to the northward! With a
cry, Lora instinctively stretched her arms toward the distant vessel;
but no sound came from her lips, for at that moment a spurt of
yellow flame rent the gray gloom, as a lantern was swung aloft to
the mast-head.
In a few seconds she would know all; for whenever the Clansman
was too late for her flag-signal to be easily seen, she showed a
green light a foot or so beneath the yellow.
Lora heard the heavy pulse of the engines, the churn of the beaten
waves, even the delirious surge and suction as the spent water was
driven along the hull and poured over and against the helm ere it
was swept into the wake that glimmered white as a snow-wreath. So
wrought was she that, at the same time, she was keenly conscious
of the rapid tweet-tweet-tweet-tweet-tweet—o-o-h sweet!—sweet!
of a yellow-hammer among the whin close by, and of the strange,
mournful cry of an oyster-opener as it flew with devious swoops
toward some twilight eyrie.
The throb of the engines—the churn of the beaten waves—the
sough of the swirling yeast—even the churning, swirling, under-
tumult, and through it and over it the heavy pulse, the deep panting

rhythmic throb: this she heard, as it were the wrought surge of her
own blood.
Would the green light never swing up to that yellow beacon?
A minute passed: two minutes: three! It was clear that the steamer
had no need to call at Innisròn. She was coming up the mid of the
Sound, and, unless the ferry-light signalled to her to draw near, she
would keep her course north-westward.
Suddenly Lora realised this. At the same time there flashed into her
mind the idea that perhaps Alastair was on board after all, but that
he was ill, and had forgotten to tell the captain of his wish to land by
the island ferry.
She turned, and, forgetful or heedless of her condition, moved
swiftly from ledge to ledge, and thence by the path to where, in the
cove beyond the clachan, the ferry-boat lay on the tide-swell,
moored by a rope fastened to an iron clank fixed in a boulder.
"Ian! Ian!" she cried, as she neared the cove; but at first she saw no
one, save Mrs. Maclean, black against the fire-glow from her
cottage. "Ian! Ian!"
A dark figure rose from beside the ferry-shed.
"Is that you, Ian? Am bheil am bhàta deas? Is the boat ready? Bi
ealamh! bi ealamh! mach am bhàta: quick! quick! out with the
boat!"
In her eager haste she spoke both in the Gaelic and the English: nor
did she notice that the old man did not answer her, or make any sign
of doing as she bade him.
"Oh, Ian, bi ealamh! bi ealamh! Faigh am bhàta deas! rach a stigh
do'n bhàta!"

Word for word, as is the wont of the people, he answered her:—
"Why is it that I should be quick? Why should I be getting the boat
ready? For what should I be going into the boat?"
"The Clansman! Do you not see her? Bi ealamh; bi ealamh! or she
will go past us like a dream."
"She has flown no flag, she has no green light at the mast. No one
will be coming ashore, and no freight; and there is no freight to go
from here, and no one who wants the ferry unless it be yourself,
Lora nighean Tormaid!"
"Alastair is there: he was to come by the steamer to-day! Be quick,
Ian! Do you hear me?"
"I hear," said the old man, as he slowly moved toward the boulder to
his left, unloosed the rope from the iron clank, and drew the boat
into the deep water alongside the landing-ledge.
"There is no good in going out, Lora bhàn! The wind is rising: ay, I
tell you, the wind goes high: we may soon hear the howling of the
sea-dogs."
But Lora, taking no notice, had sprung into the boat, and was
already adjusting the long oars to the old-fashioned wooden thole-
pins. Ian followed, grumblingly repeating, "Tha gaoth ruhòr am! Tha
coltas stairm' air!"
Once, however, that the wash of the sea caught the wherry, and the
shrewd air sent the salt against their faces, the old man appeared to
realise that the girl was in earnest. Standing, he laid hold of the
sloped mast, to steady himself against the swaying as the tide
sucked at the keel and the short waves slapped against the bows,
and then gave a quick calculating glance seaward and at the
advancing steamer.

Rapidly he gave his directions to Lora to take the helm and to keep
the boat to windward:
"Gabh an stiuir, Lora: cum ris a' ghàoth i!"
The next moment the long oars were moving slowly, but powerfully,
through the water, and the ferry-boat drove into the open, and there
lay over a little with the double swing of wind and tide.
The gloaming was now heavy upon the sea; for a mist had come up
with the dipping of the sun, and thickened the dusk.
Suddenly Ian called to Lora to hold the oars. As soon as she had
caught them, and was steadying the boat in the cross surge of the
water, he lifted a lantern from under the narrow fore-deck, lighted
the wick below the seat (after the wind had twice blown the flame
into the dark), and then, gripping the mast, waved the signal to and
fro overhead.
It was well he thought of this, for the steamer was going at full
speed, and would not have slackened.
In a few minutes thereafter the heavy stertorous throb and splash
was close by them, while the screw revolved now at quarter-speed.
A hoarse voice came from the Clansman:
"Ferry ahoy!"
"Ay, ay, ta ferry she will pe," called back Ian in the quaint English of
which he was so proud: though he thought the language a poor, thin
speech, and fit only for folk who never left the mainland.
"What are ye oot for, Ian? Ha' ye ony body comin' aboard?"
"We've come out for Mr. Alastair Macleod," Lora broke in eagerly:
"we've come to take him off."

"Hoots, my girl, what for d'ye fash yersel an' us too for the like o' sic
havers. There's no one aboard who wants to land at Innisròn: an' as
for Alastair Macleod, he was na' on the Clansman when we left
Greenock, so he could na' well be on her the now! As for you, Ian
Maclean, are ye doited, when, wi' neither flag nor green light aloft,
ye stop the steamer like this, a' for a lassie's haverin'! Ye'll hear o'
this yet, my man, I'se telling ye! Auld fule that ye are, awa' wi' ye!
keep aff the wash o' the steamer: ... an' by the Lord, I'll ..."
But already the Clansman was forging ahead, and the second-
officer's menace was swallowed up in the tumult of churned seas.
A minute later the steamer was a dark mass to the nor'-west, with a
sheet of white writhing after her, and a swirl of flaming cinders from
her funnel riding down the night like a shoal of witch-lights.
The wherry rocked heavily, caught as she was in the surge from the
screw, and lying adrift in the sliding hollows and rough criss-cross of
the waves.
Lora sat motionless and speechless. The old man stared down into
the darkness of the boat: but though his lips moved continuously, no
sound came from them.
For a time it was as though a derelict were the sport of the sea,
which had a dull moan in it, that partly was from the stifled voice of
the tide as it forced its way from the cauldrons of the deep, and
partly from the fugitive clamour of breaking waves, and mostly from
the now muffled, now loud and raucous sough of the wind as it
swung low by the surge, or trailed off above the highest reach of the
flying scud.
At last, in a whisper, the girl spoke.
"Ian, has aught of evil come to Alastair?"
"God forbid!"

"Do you know anything to his undoing?"
"No, Lora bhàn."
"You have not had the sight upon him lately?"
The islesman hesitated a moment. Raising his eyes at last, he
glanced first at his companion and then out into the dusk across the
waves, as though he expected to see some one or something there
in answer to his quest.
"I dreamt a dream, Lora, wife of Alastair. I saw you and him and
another go away into a strange place. You and the other were as
shadows; but Alastair was a man, as now, though he walked through
mist, and I saw nothing of him but from the waist upward."
Silence followed this, save for the wash of the sea, the moan of wind
athwart wave, and the soft rush of the breeze overhead.
Ian rose, and made as though he were going to put out the oars;
but as he saw how far the boat had drifted from the shore, and what
a jumble of water lay between them and the isle, he busied himself
with hoisting the patched brown sail.
As if no interval had occurred, Lora abruptly called him by name.
"Ian," she added, "what does the mist mean? ... the mist that you
saw about the feet and up to the waist of Alastair?"
There was no reply. Ian let go the sail, secured it, and then seated
himself a few feet away from Lora.
She repeated the question: but the old man was obstinately silent,
nor did he speak word of any kind till the wherry suddenly
slackened, as she slipped under the lee of the little promontory of
the landing-place.

"The tide will be on turning now," he exclaimed in his awkward
English, chosen at the moment because he did not dare to speak in
the Gaelic, fearful as he was of having any further word with his
companion; "and see, after all, the wind she will soon pe gone."
Lora, who had mechanically steered the boat to its haven, still sat in
the stern, though Ian had stepped on to the ledge and was holding
the gunwale close to it so that she might step ashore with ease. She
looked at him as though she did not understand. The old man
shifted uneasily. Then his conscience smote him for having used the
cold, unfriendly English instead of the Gaelic so dear to them both:
for was not the girl in the shadow of trouble, and did he not foresee
for her more trouble to come? So, in a gentle, apologetic voice, he
repeated in Gaelic what he had said about the tide and the wind:
"Thill an sruth: Dh' fhalbh a' ghàoth."
"There will be peace to-night," he added. "It was but a sunset
breeze, after all. There will be no storm. I think now there will be a
calm. It will be bad for the herring-boats. It is a long pull and a hard
pull when the water sleeps against the keel. A dark night, too, most
likely."
Lora rose, and slowly stepped on shore. She took no notice of Ian's
sudden garrulity. She did not seem to see him even.
He looked at her with momentary resentment: but almost
simultaneously a pitiful light came into his eyes.
"He will be here to-morrow," he murmured, "and if not, then next
day for sure."
Lora moved up the ledge in silence.
In the middle of the cove she stopped, waved her hand, and, in a
dull voice bidding good-night, wished sound sleep to him:

"Beannachd leibh! Cadal math dhiubh!"
Ian answered simply, "Beannachd leibh!" and turned to fasten the
rope to the iron clamp.
The dew was heavy, even on the rough salt spear-grass which
fringed the sand above the cove. On the short sheep-grass, on the
rocky soil beyond, it was dense, and shone white as a shroud in a
dark room. A bat swung this way and that, whirling silently. The fall
of the wind still sighed in the bent rowan trees to the west of the
clachan, where the pathway diverged from the shore. Against the
bluff of Cnoc-an-Iolair it swelled intermittently: its voice in the
hollows and crevices of the crag broken up in moans and short
gasps, fainter and fainter.
Lora noted all this wearily as she advanced. She was conscious, also,
of the nibbling of the sheep, quenching their thirst with the wet
grass: of the faint swish of her feet going through the dew: of the
dark track, like a crack in black ice, made wherever she walked in
the glisten. But though she saw and unwittingly noted, her thoughts
were all with Alastair and with what had kept him.
In her remote life there was scarce room for merely ordinary
vicissitudes. It was not a thing to ponder as ominous that one should
go out to sea after herring or mackerel and not return that night or
the morrow, or even by the next gloaming, or second dawn; or that
a man should go up among the hills and not come back for long
after his expected hour. But that one could miss the great steamer
was a thing scarce to believe in. To Lora, who had been so little on
the mainland, and whose only first-hand knowledge of the feverish
life of towns was derived from her one winter of school-life at
Rothesay and brief visits to Greenock and Oban, it was difficult to
realise how any one could fail to leave by the steamer, unless ill or
prevented by some serious mischance. The periodical coming of the
Clansman symbolised for her, to a certain extent, the inevitable
march of time and fate. To go or come by that steam-driven, wind-

heedless vessel was to be above the uncertainties and vicissitudes to
which ordinary wayfaring mortals are subject. The girl thought she
knew so much that to her all of what town-life meant must be bare,
because of her reading: knowing not that, with a woman whose
heart aches, a tear will drown every word writ in any book, a sigh
scatter the leaves into nothingness.
Deep was the puzzle to her as she slowly ascended the path which
led to Mary Maclean's cottage. She stopped once or twice, half
unconsciously, to smell the fragrance of the bog-myrtle where the
gale grew in tufts out of the damper patches, or of the thyme as it
was crushed under her feet and made over-sweet, over-poignant by
the dew.
The peat-reek reached her nostrils from the cottage, blent with the
breaths of the cows that still loitered afoot, munching the cool
wilding fodder. Her gaze, too, fell upon the fire-lit interior, with a
table overspread by a white cloth, flushed by the glow that wavered
from betwixt the red-hot bars; and, later, upon the figure of Mrs.
Maclean, who had come out to meet her, or, more likely, had been
there ever since the ferry-boat had gone off upon its useless errand.
"Are you wet, Lora? Are you cold?" she asked, as the girl drew near.
There was no need to say aught of the bitter disappointment, any
more than to speak of the glooming of the dusk: both were obvious
facts beyond the yea or nay of speech.
"I am very tired, Mary."
"Come in, dear, and have your tea. It will do you good. Lora-mo-
ghràidh, you should not have gone out in the ferry-boat. It was no
use, and the sea was rough, and you might have come to harm; and
what would Alastair Macleod be saying, to-morrow, if he found his
heart's-delight ill, and that I had stood by and seen her do so foolish
a thing?"
"Oh, Mary, do you really think he will be here to-morrow?"

"Surely."
"But I fear he will wait now till the next sailing of the Clansman."
"We cannot say. Come in, my fawn, out of the chill."
"It is going to be a lovely night. The wind falls fast; even now it is
almost still. The purple peace will be upon everything to-night. I am
restless: I do not wish to go indoors."
"No, no, Lora dear to me! Come in and have your tea, and then rest.
You can rise at daybreak, if you will, and go round the island, lest he
should be coming in any of the herring-smacks."
"I want to speak to Ian."
"Ian has gone across to Ivor Maquay's; he will not be here to-night."
Lora looked suspiciously at the speaker. Had she not left Ian a few
minutes ago, and was he not even now following her? She stared
about her, but saw no one. In the gloaming she could just descry the
black mass of the wherry. Ian was nowhere visible. She did not think
of scrutinising the shadow of the beached and long disused coble
which lay a few yards away. Had she done so, she might have
perceived the old islesman standing rigid. He had overheard his
kinswoman, and understood. As soon as the two women had
entered the cottage, he moved swiftly and silently away, and,
traversing the clachan, was soon swallowed up of the darkness.
After the meal was ended, Lora found herself overworn with
excitement. All wish to go out again went from her. From where she
lay resting, she watched Mrs. Maclean put away the things and then
seat herself by the fire.
For a long time neither woman spoke. A drowsy peace abode upon
the threshold.

The hot red glow of the peats shone steadily.
At first there had been a little lamp on the table, but after a time
Mrs. Maclean had extinguished it. Instead, she had thrown upon the
fire a log of pinewood. The dry crackle, the spurt of the sap as it
simmered in the heat, the yellow tongues and sudden red fangs and
blue flames, gave the sound and glow whereof a sweeter silence can
be wrought into what has been but stillness before.
An hour went by. With brief snatches of talk, all made up of fears
and hopes, another hour passed. Then a long quietness again,
broken at the last by a low crooning song from the elder woman, as
she leaned to the fire and stared absently into its heart. The song
was old: older than the oldest things, save the summits of the
mountains, the granite isles, and the brooding pain of the sea. Long
ago it had been sung by wild Celtic voices, before ever spoken word
was writ in letters—before that again, mayhap, and caught perhaps
from a wailing Pictish mother—so ancient was the moving old-world
strain, so antique the words of the lullaby that was dim with age
when it soothed to sleep the child Ossian, son of Fingal.
When the crooning died away, Lora slept. With soft step Mrs.
Maclean moved across the room, and lightly dropped a plaid over
the girl's figure, recumbent in beautiful ease upon the low bed-
couch.
She returned slowly to her place by the fire. After a while she was
about to seat herself, when she started violently. Surely that was a
face pressed for a moment against the window?
With a strange look in her eyes, she reproved herself for her nervous
folly. She sat down, with gaze resolutely fixed on the glowing peats:
nor would she have stirred again, but for a sound as of a low moan.
The blood ran chill in her veins; her mouth twitched; and the
intertwisted fingers of her hands were white and lifeless with the
fierce grip that came of her fear.

But she was not a woman to be mastered by terror. With a quivering
sigh she rose, looked round the room, forced herself to stare fixedly
at the window, and then moved quietly to the door.
As soon as she felt the air upon her brows she became calm, and all
dread left her.
"Is that you, Ian?" she whispered.
There was no one visible; no sound.
"Is that you, Alastair Macleod?"
So low was the utterance that, if any one had been there, he could
scarce have heard it.
To her strained ears it was as though she heard a light susurrus of
brushed dew: but it might be a wandering breath of air among the
gale, or an adder moving through the grass, or a fern-owl hawking
under the rowan-trees.
She waited a little; then, with a sigh of relief, re-entered the cottage
and closed the door.
A glance at Lora showed her that the girl was sleeping unperturbed.
For some time there after she sat by the fire, brooding over many
things. Weary, at last, she rose, cast a farewell glance at the sleeper,
and then slipped quietly to her bed in the adjoining room.
Night lay passively upon the sea, upon the isle, upon the clachan.
Not a light lingered in any cottage, save the fire-glow in that of Mary
Maclean: a hollow, attenuating beam that stared through the dark
unwaveringly.
Neither star nor moon was visible. The clouds hung low, but without
imminence of rain for the isles, drawn inland as the vapours were by
the foreheads of the bens.

An hour later the door of the cottage opened and closed again,
silently. It was Lora who came forth.
She walked hesitatingly at first, and then more swiftly, not pausing
till she reached the little boulder-pier. There she stood motionless,
listening intently.
The water lapped among the hollows, above which the ebb-left
shellfish gaped thirstily. There was a lift among the dulse-heaps, as
though a finger stirred them and let loose their keen salt smells. The
bladder-wrack moved with strange noises, sometimes startlingly
loud, oftenest as if sea-things were being stifled or strangled.
From the promontory came a cry: abrupt, strident—the hunger-note
of a skua. The thin pipe of the dotterel fell into the darkness beyond
the shallows where the sea-mist lay. In the Kyle a muffled,
stertorous breath, near and twice as far away, told that two whales
were in the wake of the mackerel.
From the isle, no sound. The sheep lay on the thyme, or among the
bracken, still as white boulders. The kye crouched, with misty
nostrils laid low to the damp grass, rough with tangled gale. The
dogs were silent. Even the tufted canna hung straight and
motionless. The white moths had, one by one, fallen like a fallen
feather. The wind-death lay upon all: at the last, too, upon the sea.

II
Slowly, as though a veil were withdrawn, the cloudy dusk passed
from the lift. The moon, lying in violet shadow, grew golden: while
the sheen of her pathway, trailed waveringly across the sea and
athwart the isle, made Innisròn seem as a beautiful body
motionlessly adrift on the deep.
One by one the stars came forth—solemn eyes watching for ever the
white procession move onward orderly where there is neither height,
nor depth, nor beginning, nor end.
In the vast stellar space the moon-glow waned until it grew cold,
white, ineffably remote. Only upon our little dusky earth, upon our
restless span of waters, the light descended in a tender warmth.
Drifting upon the sea, it moved tremulously onward, weaving the
dark waters into a weft of living beauty.
Strange murmur of ocean, even when deep calm prevails, and not
the most homeless wind lifts a weary wing from wave-gulf to wave-
gulf. As a voice heard in dream; as a whisper in the twilight of one's
own soul; as a breath, as a sigh from one knows not whence, heard
suddenly and with recognising awe; so is this obscure, troublous
echo of a tumult that is over, that is not, but that may be, that
awaiteth.
To Lora it was almost inaudible. Rather, her ears held no other sound
than the babbling repetitive chime and whisper of the lip of the sea
moving to and fro the pebbles on the narrow strand just beyond her.

Her eyes saw the lift of the dark, the lovely advance of the lunar
twilight, the miracle of the yellow bloom—golden here and here
white as frost-fire—upon sea and land: they saw, and yet saw not.
Her ears heard the muffled voice of ocean and the sweet recurrent
whispering of the foam-white runnels beside her: they heard, and
yet heard not.
Surely, in the darkness, in the loneliness, she would have knowledge
of Alastair. Surely, she thought, he would come to her in the spirit. In
deep love there is a living invisible line from soul to soul whereby
portent of joy or disaster, or passion of loneliness, or passion of fear,
or passion of longing may be conveyed with terrifying surety.
How beyond words dreadful was this remoteness which environed
her, as the vast dome of night to a single white flower growing
solitary in a waste place.
Inland upon the isle, seaward, skyward, Lora looked with aching
eyes. The moonlight wounded her with its peace. The shimmering
sea beat to a rhythm atune to a larger throb than that of a petty
human life. In the starry infinitude her finitude was lost, absorbed,
as a grain of sand wind-blown a few yards across an illimitable
desert.
That passionate protest of the soul against the absolute unheed of
nature was hers: that already defeated revolt of the whirling leaf
against the soaring, far-come, far-going wind that knows nothing of
what happens beneath it in the drift of its inevitable passage.
With a sob, she turned, vaguely yearning for the human peace that
abode in the cottage. As she moved, she saw a shadow, solidly
clear-cut in the moonlight, sweep from a rock close by, as though it
were a swinging scythe.
Instinctively she glanced upward, to see if the cloud-counterpart
were overhead. The sky was now cloudless: neither passing vapour

nor travelling wild-swan had made that shadow leap from the
smooth boulder into the darkness.
She trembled: for she feared she had seen the Watcher of the Dead.
At the wane of the last moon, an old islesman had passed into the
white sleep. Lora knew that his spirit would have to become the
Watcher of Graves till such time as another soul should lapse into
the silence. Was this he, she wondered with instinctive dread—was
this Fergus, weary of his vigil, errant about the isle which had been
the world to him, a drifting shadow from graveyard to byre and
sheiling, from fold to dark fold, from the clachan-end to the shore-
pastures, from coble to havened coble, from the place of the boats
to the ferry-rock? Did he know that he would soon have one to take
over from him his dreadful peace? Or was he in no satiate peace,
but anhungered as a beast of prey for the death of another? And
then ... and then ... who was this other? Who next upon the isle
would be the Watcher of the Dead?
With a low, shuddering breath, she sighed, "Fergus!"
The fall of her voice through the silence was an echo of terror. She
clasped her hands across her breast. Her body swayed forward as a
bulrush before the wind.
"Ah, Dia! Dia!" broke from her lips; for, beyond all doubt, she saw
once again the moving of a darkness within the dark.
Yet what she saw was no shadow-man weary of last vigil, but
something that for a moment filled her with the blindness of dread.
Was it possible? Was she waylaid by one of those terrible dwellers in
twilight-water of which she had heard so often from the tellers of old
tales?
"Toradh nu féudalach gun am faicinn," she muttered with cold lips:
"the offspring of the cattle that have not been seen!"

"Ah, no, no!" she cried. The next moment, and with a sob of relief,
she saw a moonbeam steal upon the hollow and reveal its quietude
of dusk. She would have moved at once from boulder to boulder,
eager for that lost sanctuary whence she had come—when the very
pulse of her heart sprang to the burst of a human sob close by.
She stood still, as though frozen. A moment before, the breath from
her lips was visible: now not the faintest vapour melted into the
night-air.
Was she dreaming, she wondered, when the stifling grip at her heart
had mercifully relaxed?
No: there was no mistake. Blent with the gurgle and cluck and
whisper of the water among the lifted bladder-wrack and in and out
of the pools and crannies in the rocks, there was the piteous sound
of a human sob.
All at once, everything became clear to Lora. She knew that Alastair
was near: she did not even dread that he was present as a
disembodied spirit. He had reached the isle after all, but in some
strange sorrow had not sought her straightway.
"Alastair!" she cried yearningly.
No one answered; no one stirred; nothing moved. But the muffled
sobbing was hushed.
"Alastair! Alastair!"
Slowly from a sand-drift beside the ferry-rock a tall figure arose. For
a few moments it stood motionless, black against the yellow shine of
the moon. The face was pale; that of a man, young, with the thin
lips, the shadowy eyes that in sunlight would shine sea-blue, the
high oval features, the tangled, curly, yellow-tawny hair of the
islesmen of the ancient Suderöer, in whose veins the Celtic and the
Scandinavian strains commingle.

Alastair was as visible as though he were in the noon-light.
Lora looked at him, speechless. She saw that in his strained eyes, in
his wrought features, which told her he had drunken of sorrow. His
dishevelled hair, his whole mien and appearance showed that he was
in some dire extremity.
"Alastair!"
He heard the low, passionate appeal, but at first he did not stir.
Then, and yet as though constrainedly and in weariness, he raised
and stretched forth his arms.
Swift as a gliding shadow, Lora was beside him, and clasped to his
heart.
For a time, neither spoke. His heart beat loud and heavily: against
his breast her head lay, with her breath coming and going like a
wounded bird panting in the green-gloom of the thicket.
"O Alastair, Alastair, what is it?" she murmured at last, raising her
head and looking into his pale, distraught face.
"What made you come out in the dark, Lora-mùirnean?"
"I could not rest. I was too unhappy. I thought—I thought—no, I do
not think I dared to believe that you might come to-night after all;
but something made me long to go down to the sea. Did you see me
only now, dear heart?"
"No, Lora."
For a moment she was still, while she gazed fixedly at Alastair.
"Ah," she whispered at last, "then you have been here all this night,
and I not knowing it! Ah, Alùinn, it was your heart crying to mine
that made me rise and leave the cottage and come out into the

dark. But why did you not come to me? When did you come to
Innisròn? How did you come?"
"Dear, I could not wait for the Clansman. I left Greenock three hours
earlier by the Foam, James Gilchrist's tug; for he undertook to put
me ashore at the haven below Craig-Sionnach. Thence I walked to
Dunmore. But I was not well, Lora; and I was so long on the way
that I missed the Clansman as well as the Dunmore herring-steamer.
Before nightfall, however, I persuaded Archibald Macleod, of
Tighnacraigh, to bring me here on his smack. I landed at the Rock of
the Seafold. It was already dusk, and my heart was against yours in
longing, my beautiful gloom: yet over me came such a sorrow that I
could not bear the homing, and so moved restlessly from shadow to
shadow. I felt as though it would be better for me to deal with my
sorrow alone and in the night, and that it was more bearable since I
was so near you, and that any moment I could go to you."
"Why, why did you not come, Alastair? Oh, I longed, longed for you
so!"
"Once I came close to the cottage, almost happy since I knew that
you were so near to me. The red glow that warmed the dark without
comforted me. I thought I would look in upon you for a moment;
and if you and Mary were awake and talking, that I should let you
know I had come. But I saw that you lay in sleep; and I had scarce
time to withdraw ere, as I feared, Mary saw me—though see me,
indeed, perhaps she did, for in a brief while she opened the door
and came out, and would have discovered me but that I moved
swiftly to the shadow of the birk-shaws. Then, after a little, I
wandered down by the shore. There was a voice in the sea—calling,
calling. It was so cool and sweet: soft was the balm of the air of it,
as the look of your eyes, Lora, as the touch of your hand. I was
almost healed of my suffering, when suddenly the pain in my head
sprang upon me, and I crouched in the hollow yonder, chill with the
sweat of my agony."

"O Alastair, Alastair, then you are no better: that great doctor you
went so far to see has done you no good?"
"And in the midst of my pain, Lora my Rest, I saw you standing by
the sea upon the ferry-ledge. At first I took you for a vision, and my
heart sank. But when the moonlight reached the isle and enfolded
you, I saw that it was you indeed. And once more my pain and my
sorrow overcame me!"
"Alastair, I am terrified! It was not thus for you before you went
away. Great as was your pain, you had not this gloom of sorrow. Oh,
what is it, what is it, dear heart? Tell me, tell me!"
Slowly Alastair held Lora back from him, and looked long and
searchingly into her eyes.
She shrank, in an apprehension that, like a bird, flew bewildered
from the blinding light that flashed out of the darkness—a vain
bewilderment of foredoom.
Then, with a great effort, she bade him tell her what he had to say.
Too well he knew there was no time to lose: that any day, any
moment, his dark hour would come upon him, and that then it
would be too late. Yet he would fain have waited.
"Lora, have you heard aught said by any one concerning my illness?"
"Dear, Father Mantus told me, on the day you went away, that you
feared the trouble which came upon your father, and upon your
father's father; and oh, Alastair my beloved, he told me what that
trouble was."
"Then you know: you can understand?"
"What?"

"That which now appals me ... now kills me."
"Alastair!"
"Yes, Lora?"
"Oh, Alastair, Alastair, you do not mean that ... that ... you too ...
you are ... are ... that you have the ... the ... mind-dark?"
"Dear heart of mine, this sorrow has come to us. I——"
With a sharp cry Lora held him to her, despairingly, wildly, as though
even at that moment he were to be snatched from her. Then, in a
passion of sobbing, she shook in his arms as a withered aspen-leaf
ere it fall to the wind.
The tears ran down his face; his mouth twitched; his long, thin
fingers moved restlessly in her hair and upon her quivering shoulder.
No other sound than her convulsive sobs, than his spasmodic
breathing, met in the quietude of whisper-music exhaled as an
odour by the sea and by the low wind among the corries and upon
the grasses of the isle.
A white moth came fluttering slowly toward them, hovering vaguely
awhile overhead, and then drifting alow and almost to their feet. In
the shadow it loomed grey and formless—an obscure thing that
might have come out of the heart of the unguarded brain. Upward
again it fluttered, idly this way and that: then suddenly alit upon the
hair of Alastair, poising itself on spread wings, and now all agleam as
with pale phosphorescent fire, where the moonlight filled it with
sheen as of white water falling against the sun.
The gleam caught Lora's eyes as, with a weary sigh, she lifted her
head.

A strange smile came into her face. Slowly she disengaged her right
arm, and half raised it. Alastair was about to speak, but her eyes
brought silence upon him.
"Hush!" she whispered at last.
He saw that her eyes looked beyond his, beyond him, as it seemed.
What did she see? The trouble in his brain moved anew at this touch
of mystery.
"What is it, Lora?"
"Hush, hush!... I see a sign from heaven upon your forehead ... the
sign of the white peace that Seumas says is upon them who are of
the company of the Belovëd."
"Lora, what are you saying? What is it? What do you see?"
His voice suddenly was harsh, fretful. Lora shrank for a moment;
then, as the white moth rose and fluttered away into the dark,
faintly agleam with moonfire till it reached the shadow, she pitifully
raised her hand to his brow.
"Come, dear, let us go in. All will be well with us, whatever
happens."
"Never ... never ... never!"
"O Alastair, if it be God's will?"
"Ay, and if it be God's will?"
"I cannot lose you; you will always be mine; no sorrow can part us;
nothing can separate us; nothing but the Passing, and that ..."
"Lora!"
For answer she looked into his eyes.

"Lora, it is of that, of the Passing: ... are you ... are you brave
enough not only to endure ... but to ... if we thought it well ... if I
asked you...?"
A deep silence fell upon both. Hardly did either breathe. By some
strange vagary of the strained mind, Lora thought the throb of her
heart against her side was like the pulse of the engines of the
Clansman to which she had listened with such intent expectation
that very evening.
From the darkness to the north came the low monotone of the sea,
as a muffled voice prophesying through the gates of Sleep and
Death. Far to the east the tide-race tore through the Sound with a
confused muttering of haste and tumult. Upon the isle the wind
moved as a thing in pain, or idly weary: lifting now from cranny to
corrie, and through glen and hollow, and among the birk-shaws and
the rowans, with long sighs and whispers where by Uisghe-dhu the
valley of moonflowers sloped to the sea on the west, or among the
reeds, and the gale, and the salt grasses around the clachan that lay
duskily still on the little brae above the haven.
"Lora ... would you ... would...?"
Only her caught breath at intervals gave answer. The short lisp and
gurgle of the water in the sea-weed close by came nearer. The tide
was on the flood, and the sand about their feet was already damp.
The immense semicircle of the sky domed sea and land with infinity.
In the vast space the stars and planets fulfilled their ordered plan.
Star by star, planet by planet, sun by sun, universe by universe
moved jocund in the march of eternal death.
Beyond the two lonely figures, seaward, the moon swung, green-
gold at the heart with circumambient flame of pearl.
Beautiful the suspended lamp of her glory—a censer swung before
the Earth-Altar of the Unknown.

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