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Control Engineering Series 95
Modelling Control
Systems Using
IEC 61499
2nd Edition
Modelling
Control
Systems
Using
IEC
61499
2nd
Edition
Zoitl
&
Lewis
Alois Zoitl & Robert Lewis
The Institution of Engineering and Technology
www.theiet.org
978-1-84919-760-1
Modelling Control Systems
Using IEC 61499
2nd Edition
Robert Lewis is a Fellow of the Institution of Engineering
and Technology (FIET) and Chartered Engineer (C Eng.).
He is an engineering safety consultant for Atkins with
experience in Safety Case development and authoring,
Hazard analysis, HAZOP workshops, FMECA, systems
assurance, safety assessment and requirements
management. He was formerly a UK expert on two IEC
working groups defining new standards for industrial
control software, covering distributed control systems (IEC
61499) and PLC software (IEC 61131).
Alois Zoitl leads the Industrial Automations research
group at the research institute fortiss in Munich, Germany.
He has conducted several research projects on distributed
adaptive automation systems and has given lectures
and consulted on IEC 61499 for more than ten years.
He is co-author of more than 100 publications and the
co-inventor of 4 patents. Dr. Zoitl is a founding member
of the open source initiatives 4DIAC and OpENer. He is a
member of the PLCopen user organization, consultant for
CAN in Automation as well as the IEC SC65B/WG15 for
the distributed automation standard IEC 61499.
IEC 61499 is a standard for modelling distributed control systems for
use in industrial automation, and is already having an impact on the
design and implementation of industrial control systems that involve
the integration of programmable logic controllers, intelligent devices
and sensors.
Modelling Control Systems Using IEC 61499. 2nd Edition provides
a concise and yet thorough introduction to the main concepts and
models defined in the standard. Topics covered include defining
applications, systems, distributing applications on the system's devices,
function blocks, structuring applications, service interface function
blocks, event function blocks, and examples of industrial applications.
This second edition has been significantly updated to reflect the
current second release of IEC 61499, including changes in the
function block model, its execution, and the newly standardized XML
exchange format for model artefacts, and to reflect lessons learned
from the author’s teaching of IEC 61499 over the last ten years. This
book will be of interest to research-led control and process engineers
and students working in fields that require complex control systems
using networked based distributed control.
Modelling Control Systems Using IEC 61499, 2nd Edition.indd 1 29/04/2014 20:51:20

IET CONTROL ENGINEERING SERIES 95
Modelling Control
Systems Using
IEC 61499

Other volumes in this series:
Volume 8 A history of control engineering, 1800–1930 S. Bennett
Volume 18 Applied control theory, 2nd edition J.R. Leigh
Volume 20 Design of modern control systems D.J. Bell, P.A. Cook and N. Munro Editors)
Volume 28 Robots and automated manufacture J. Billingsley (Editor)
Volume 33 Temperature measurement and control J.R. Leigh
Volume 34 Singular perturbation methodology in control systems D.S. Naidu
Volume 35 Implementation of self-tuning controllers K. Warwick (Editor)
Volume 37 Industrial digital control systems, 2nd edition K. Warwick and D. Rees Editors)
Volume 39 Continuous time controller design R. Balasubramanian
Volume 40 Deterministic control of uncertain systems A.S.I. Zinober (Editor)
Volume 41 Computer control of real-time processes S. Bennett and G.S. Virk (Editors)
Volume 42 Digital signal processing: principles, devices and applications N.B. Jones and
J.D.McK. Watson (Editors)
Volume 44 Knowledge-based systems for industrial control J. McGhee, M.J. Grimble and
A. Mowforth (Editors)
Volume 47 A history of control engineering, 1930–1956 S. Bennett
Volume 49 Polynomial methods in optimal control and filtering K.J. Hunt (Editor)
Volume 50 Programming industrial control systems using IEC 1131-3 R.W. Lewis
Volume 51 Advanced robotics and intelligent machines J.O. Gray and D.G. Caldwell (Editors)
Volume 52 Adaptive prediction and predictive control P.P. Kanjilal
Volume 53 Neural network applications in control G.W. Irwin, K. Warwick and K.J. Hunt (Editors)
Volume 54 Control engineering solutions: a practical approach P. Albertos, R. Strietzel and
N. Mort (Editors)
Volume 55 Genetic algorithms in engineering systems A.M.S. Zalzala and P.J. Fleming (Editors)
Volume 56 Symbolic methods in control system analysis and design N. Munro (Editor)
Volume 57 Flight control systems R.W. Pratt (Editor)
Volume 58 Power-plant control and instrumentation: the control of boilers and HRSG systems
D. Lindsley
Volume 59 Modelling control systems using IEC 61499 R. Lewis
Volume 60 People in control: human factors in control room design J. Noyes and M. Bransby
(Editors)
Volume 61 Nonlinear predictive control: theory and practice B. Kouvaritakis and M. Cannon (Editors)
Volume 62 Active sound and vibration control M.O. Tokhi and S.M. Veres
Volume 63 Stepping motors, 4th edition P.P. Acarnley
Volume 64 Control theory, 2nd edition J.R. Leigh
Volume 65 Modelling and parameter estimation of dynamic systems J.R. Raol, G. Girija and J. Singh
Volume 66 Variable structure systems: from principles to implementation A. Sabanovic,
L. Fridman and S. Spurgeon (Editors)
Volume 67 Motion vision: design of compact motion sensing solution for autonomous systems
J. Kolodko and L. Vlacic
Volume 68 Flexible robot manipulators: modelling, simulation and control M.O. Tokhi and
A.K.M. Azad (Editors)
Volume 69 Advances in unmanned marine vehicles G. Roberts and R. Sutton (Editors)
Volume 70 Intelligent control systems using computational intelligence techniques A. Ruano
(Editor)
Volume 71 Advances in cognitive systems S. Nefti and J. Gray (Editors)
Volume 72 Control theory: a guided tour, 3rd edition J. R. Leigh
Volume 73 Adaptive sampling with mobile WSN K. Sreenath, M.F. Mysorewala, D.O. Popa and
F.L. Lewis
Volume 74 Eigenstructure control algorithms: applications to aircraft/rotorcraft handling
qualities design S. Srinathkumar
Volume 75 Advanced control for constrained processes and systems F. Garelli, R.J. Mantz and
H. De Battista
Volume 76 Developments in control theory towards glocal control L. Qiu, J. Chen, T. Iwasaki and H.
Fujioka (Editors)
Volume 77 Further advances in unmanned marine vehicles G.N. Roberts and R. Sutton (Editors)
Volume 78 Frequency-domain control design for high-performance systems J. O’Brien
Volume 81 Optimal adaptive control and differential games by reinforcement learning
principles D. Vrabie, K. Vamvoudakis and F. Lewis
Volume 88 Distributed control and filtering for industrial systems M. Mahmoud
Volume 89 Control-based operating system design A. Leva et al
Volume 90 Application of dimensional analysis in systems modelling and control design
P. Balaguer
Volume 91 An introduction to fractional control D. Valério and J. Costa
Volume 92 Handbook of vehicle suspension control systems H. Liu, H. Gao & P. Li

Modelling Control
Systems Using
IEC 61499
2nd Edition
Alois Zoitl and Robert Lewis

Published by The Institution of Engineering and Technology, London, United Kingdom
The Institution of Engineering and Technology is registered as a Charity in England &
Wales (no. 211014) and Scotland (no. SC038698).
† 2001, 2014 The Institution of Engineering and Technology
First published 2001
Second Edition 2014
This publication is copyright under the Berne Convention and the Universal Copyright
Convention. All rights reserved. Apart from any fair dealing for the purposes of research
or private study, or criticism or review, as permitted under the Copyright, Designs and
Patents Act 1988, this publication may be reproduced, stored or transmitted, in any
form or by any means, only with the prior permission in writing of the publishers, or in
the case of reprographic reproduction in accordance with the terms of licences issued
by the Copyright Licensing Agency. Enquiries concerning reproduction outside those
terms should be sent to the publisher at the undermentioned address:
Michael Faraday House
Six Hills Way, Stevenage
Herts, SG1 2AY, United Kingdom
www.theiet.org
While the authors and publisher believe that the information and guidance given in this
work are correct, all parties must rely upon their own skill and judgement when making
use of them. Neither the authors nor publisher assumes any liability to anyone for any
loss or damage caused by any error or omission in the work, whether such an error or
omission is the result of negligence or any other cause. Any and all such liability is
disclaimed.
The moral rights of the authors to be identified as authors of this work have been
asserted by them in accordance with the Copyright, Designs and Patents Act 1988.
British Library Cataloguing in Publication Data
A catalogue record for this product is available from the British Library
ISBN 978-1-84919-760-1 (hardback)
ISBN 978-1-84919-761-8 (PDF)
Typeset in India by MPS Limited
Printed in the UK by TJ International Ltd, Cornwall

Contents
Foreword ix
Foreword xi
Preface xiii
Abbreviations and conventions xvii
1 Introduction 1
1.1 IEC 61499 function block standard 5
1.2 Development of function block concept beyond IEC 61131-3 8
1.2.1 Global variables 10
1.2.2 Communications function blocks 11
1.3 Development of IEC 61499 12
1.4 Why use function blocks 14
1.5 System design views 16
1.5.1 Logical view 17
1.5.2 Process view 17
1.5.3 Development view 18
1.5.4 Physical view 18
1.5.5 Scenarios 18
1.6 The future beyond IEC 61499 19
2 IEC 61499 models and concepts 21
2.1 Function block model 22
2.1.1 General characteristics 22
2.1.2 Execution model for function blocks 24
2.1.3 Function block types 27
2.2 Application model 28
2.3 System model 29
2.3.1 Overall system structure 29
2.3.2 Device model 30
2.3.3 Resource model 30
2.4 Distribution model 32
2.4.1 Mapping of applications 32
2.4.2 Platform specific configurations 34
2.5 Management model 34
2.5.1 Management applications 36
2.5.2 Operational state model of managed entities 37

2.6 Exchange format for IEC 61499 entities 39
2.6.1 Textual syntax for IEC 61499 entities 39
2.6.2 XML-exchange format 41
2.7 Summary 43
3 Defining function block types 45
3.1 Types and instances 45
3.2 Different form of function blocks 45
3.3 External interface declaration 46
3.3.1 Static interface declaration 47
3.3.2 Defining the dynamic interface behaviour 48
3.3.3 2 out of 3 voter example 50
3.4 Defining basic function blocks 53
3.4.1 Internal behaviour 53
3.4.2 Execution control chart features 55
3.4.3 Execution of basic function blocks 56
3.4.4 Behaviour of instances of basic function blocks 59
3.4.5 Basic function block examples 59
3.5 Definition composite function blocks 62
3.5.1 Rules for composite function block type specification 62
3.5.2 Execution of composite function blocks 64
3.5.3 Composite function block example 64
3.6 Summary 68
4 Structuring applications 69
4.1 Application structuring with subapplications 69
4.1.1 Rules for subapplication type specification 71
4.1.2 Rules for subapplication execution 72
4.1.3 Subapplication example 72
4.1.4 Subapplication distributed example 74
4.1.5 Guidelines for using subapplications 77
4.2 Structured interfaces using adapters 78
4.2.1 Adapter concept 79
4.2.2 Defining adapter types 81
4.2.3 Modelling the behaviour of adapter types 82
4.2.4 Using adapter types in function blocks 83
4.2.5 Adapter interface usage example 85
4.2.6 Guidelines for using adapters 88
4.3 Summary 88
5 Service interface function blocks 91
5.1 Overview 91
5.2 Interface specifications 93
5.2.1 Standard inputs and outputs for service interface
function blocks 93
vi Modelling control systems using IEC 61499

5.2.2 Service sequence diagrams for service
interface function blocks 94
5.3 Type definitions 98
5.3.1 General service interface function block types 98
5.3.2 Example service interface function block types 100
5.3.3 Textual syntax – service interface function block example 101
5.4 Communication service interface function blocks 103
5.4.1 Function blocks for unidirectional transactions 103
5.4.2 Function blocks for bidirectional transactions 104
5.5 Management function blocks 106
5.5.1 Examples 108
5.5.2 Managed function blocks 108
5.6 Summary 109
6 Event function blocks 111
6.1 Overview 111
6.2 Standard event function block types 113
6.2.1 Event Splitter 114
6.2.2 Event Merger 114
6.2.3 Two Event Rendezvous 114
6.2.4 Permissive Event Propagator 116
6.2.5 Event Selector 116
6.2.6 Event Switch 117
6.2.7 Delayed Event Propagator 117
6.2.8 Restart Event Generator 118
6.2.9 Cyclic Event Generator 118
6.2.10 Event Train Generator 119
6.2.11 Event Train Table-driven Generator 120
6.2.12 Separate Event Table-driven Generator 121
6.2.13 Event-driven Bistable 122
6.2.14 D (data latch) Bistable 123
6.2.15 Boolean Rising Edge Detector 123
6.2.16 Boolean Falling Edge Detector 124
6.2.17 Event-driven Up Counter 125
6.3 Using event function blocks for event flow control 125
6.3.1 Basic event flow control 125
6.3.2 Conditional event propagation 127
6.3.3 Modelling control tasks 128
6.4 Summary 129
7 Industrial application examples 131
7.1 Overview 131
7.2 Temperature control example 132
7.3 Conveyor test station example 135
7.3.1 Distributed system model 141
Contents vii

7.4 Fieldbus applications 143
7.4.1 Analogue input function block example 146
7.4.2 Further generalisation of the analogue input
function block 151
7.5 Concluding remarks 153
7.6 Summary 154
8 Epilogue 155
8.1 Current status of IEC 61499 155
8.2 Engineering Support Task 157
8.3 Compliance to IEC 61499 159
8.3.1 IEC 61499 compliance profiles 159
8.3.2 Device classes 160
8.4 Large-scale industrial applications 161
8.5 Summary 162
Appendix A Common elements 165
Appendix B IEC 61499 Compliance Profile for Feasibility
Demonstrations 175
Appendix C Frequently asked questions (IEC 61499 FAQ) 181
Appendix D PID function block example 191
Appendix E Exchange formats 207
Appendix F Bibliography 219
Index 221
viii Modelling control systems using IEC 61499

Foreword
In early 1990, Technical Committee 65 of the International Electrotechnical
Commission (IEC TC65) initiated a project to develop a common architectural
model for the application of software modules called ‘function blocks’ in dis-
tributed industrial-process measurement and control systems (IPMCS). This model
was to encompass IPMCS utilising ‘Fieldbus’ systems as specified in IEC 61158 as
well as IPMCS utilising the programming languages defined in Part 3 of the IEC
61131 standard for programmable controllers. This project resulted in the current
IEC 61499 standard for function blocks.
Due to the relative immaturity of the IEC 61158 project at the time of the
proposal, experts and a project leader were not available for the 61499 project until
approximately two years after its inception, at which time the first edition of IEC
61131-3 was also completed and available for reference. Because of the close
relationship between IEC 61131-3 and the projected IEC 61499, many of the
experts participating in the development of the latter came from the previous
61131-3 project, including Bob Lewis and myself.
Through a long process of systematic application of software engineering
and open systems principles, with intensive international review and revision, the
TC65/WG6 experts reached consensus on the basic concepts and detailed technical
approach to the resolution of a number of fundamental issues. This resulted in the
publication in 2002-4 of IEC/PASs (Publicly Available Specifications) 61499-1, -2
and -4, for a two-year period of trial implementations, as well as IEC/TR 61499-3
containing tutorial information. This initial consensus was reflected and thoroughly
explained in the first edition of the present book.
In the years to follow, the accumulation of experience in the adoption and
implementation of IEC 61499 resulted in the publication of 61499-1, -2 and -4 as
IEC Standards in 2005, and in second edition in 2012. Alois Zoitl was a key
member of the IEC working group during this period, as well as being one of the
prime developers of the widely used 4DIAC open-source software tool and runtime
platform for the development and implementation of IEC 61499 applications.
I would like to express my gratitude to Bob and Alois for bringing out this
updated edition of Bob’s pioneering book on IEC 61499. It is my hope that this will
provide the basic information needed to promote the ongoing industrial adoption
of IEC 61499, as well as serving as a textbook for courses in advanced industrial
process automation and control.
James H. Christensen
Cleveland Heights, Ohio USA
14 December 2013

Modelling Control Systems Using IEC 61499 2nd ed. 2014 Edition Alois Zoitl

Foreword
Is our birthday which we celebrate every year an event or a cyclic event?
Unlike in normal life, in industrial automation, we have a standard leading the way,
namely IEC 61499.
The question of event-driven versus cyclic execution is a topic that is most
discussed between the IEC 61131-3 and IEC 61499 representatives. However, in
our experience, the customer is not interested in events or cycles, but in solutions
to his problems in an increasingly networked, distributed and complex world.
In addition it should be mentioned that the IEC 61499 and IEC 61131-3 standards
are close relatives. They share the same roots but have a different scope and purpose.
So someone who is familiar with IEC 61131-3 will also cope with IEC 61499 and
appreciate it.
At the point of intersection, where an old technology is slowly being replaced
by a new technology, it is most challenging. The cards are reshuffled and some-
times new opportunities arise. This is the time for pioneers, who look outside the
box and develop ideas and upcoming solutions, resulting in a clear competitive
edge. Anybody who, in addition, closely watches the industrial users, sharpens their
view on real problems to develop their vision further. This is important if one is in
the process of developing a product that relies on a new technology, which should
be better than anything ever offered before.
Developing our vision and creating it as a marketable product was a long
journey and at the beginning of this journey was the first edition of this book. It
provides a solid foundation and is a good accompaniment for the practical imple-
mentation of one’s ideas. The foundations are there, but the creativity in the
implementation is, of course, the role of the system designer.
Already today we can claim and prove that IEC 61499 is the better solution for
many tasks in automation, particularly for building automation, process automation,
and machine control but also in the field of intelligent energy networks (e.g. smart
grids based on IEC 61850). This is also reflected by the increasing interest in the
market. This dynamic will bring a demand for people with expertise in the field of
IEC 61499. With this growth in know-how, the spread and importance of the stan-
dard will increase at the same time. This book provides, therefore, the perfect start.
Finally, we would like to raise an appeal to current and future IEC 61499
vendors:
Keep compatibility high, in the long term it will be worthwhile for vendors
and users alike!

Many thanks to all who supported, with their know-how, perseverance and
passion, the development of the IEC 61499 standard and last, but not least, also to
the authors of this book.
Horst Mayer (CTO nxtControl)
Arnold Kopitar (CEO nxtControl)
Leobersdorf, Austria
17 December 2013
xii Modelling control systems using IEC 61499

Preface
New technologies and standards are emerging that are set to have a dramatic effect
on the design and implementation of industrial control systems. These technologies
will reduce the time to bring new systems onstream, and leverage the integration of
business and industrial systems.
There is currently an explosion in the use of Object-Oriented (OO) software
encapsulated as components. In business systems, the use of software components
and technology together with service-oriented architectures is becoming more
widespread. In industrial systems, programmable logic controllers (PLCs) and soft
controllers based on Personal Computer (PC) architectures are also starting to adopt
many of these techniques. The different worlds of factory automation and business
systems are clearly starting to share the same software technology.
With so much scope for complexity new tools and techniques are clearly
needed to design and model such systems. To date, new methodologies have
emerged, such as the Unified Modelling Language (UML), which allow software
engineers to deal with the complexity of OO-based systems.
Control and system engineers are also faced with increased software com-
plexity as advances in industrial networking, such as Fieldbus and Industrial
Ethernet technologies, allow intelligence to be distributed throughout the system
from controllers, instruments, actuators and even out to the sensors themselves. As
these systems become more complex, new tools and techniques are needed to
model their behaviour.
Some of this complexity can be dealt with effectively by use of the IEC 61499
standard. It has been developed specifically as a methodology for modelling dis-
tributed industrial process measurement and control systems. This standard defines
concepts and models so that software components in the form of function blocks
can be interconnected to define the behaviour of a distributed industrial process
measurement and control system.
Process and system engineers have used function blocks in various forms for a
number of years as an effective way to represent and model software functionality
in instrumentation and controllers. The PID algorithm is probably the best example
of an early form of function block. New forms of smart devices and sensors now
allow intelligence to be distributed widely throughout a control system. It is now
becoming more difficult to define where the main intelligence of any control sys-
tem really resides; intelligence is becoming truly distributed.
Tools based on the IEC 61499 standards are emerging that can model, validate
and simulate the behaviour of complex function block networks. IEC 61499 defines

a completely new development methodology, which requires a rethinking of con-
trol engineers. It has been in development for a number of years by international
experts working in the field of control system software. It is set to become an
important methodology for the process and system engineers working with com-
plex distributed systems.
The main objective of this book is to widen the understanding of the most
important concepts in the IEC 61499 standard and to show how these concepts can be
applied to industrial problems. IEC 61499 is a complex standard that defines many
new concepts related to function blocks and the supporting architecture in a rigorous
and thorough manner – as a consequence, the standard can be difficult to understand
by people who read it for the first time. This book has therefore concentrated on the
main concepts and has intentionally summarised or omitted some of the less sig-
nificant details in the standard. For this reason, some topics such as the Textual
Syntax for describing function block definitions have not been covered in great detail.
IEC 61499 provides, for the first time, a framework and architecture for
describing the functionality in distributed control systems in terms of co-operating
networks of function blocks. It is the authors’ intention that the benefits of this
standard should be understood by a wide audience; including not only people
working in industrial control and also those with a general interest in methodolo-
gies for modelling distributed systems.
Major progress since the first edition
Since the publication of the first edition of the book, many things have happened in
the world of IEC 61499. The most prominent are as follows:
● The standard IEC 61499 has gone through two major revisions – when it was
initially published as international standard in 2005 and then again when it
was revised in the second edition in 2012. Many concepts have been refined,
errors corrected and ambiguities clarified.
● At the time when the first edition was written only one prototype software tool,
which supported the evaluation of the models and concepts of IEC 61499, was
available. Since then several tools and runtime platforms have been developed.
Now free, commercial and open source implementations, allowing the devel-
opment of distributed industrial process measurement and control systems, are
available.
● In the last 14 years much research has been focused on topics of IEC 61499.
Investigated topics have included the execution of IEC 61499 models, devel-
opment methodologies, formal verification methods and communication
aspects – just to name the most prominent. This research has completely
changed and improved how we now understand and use IEC 61499.
● We have been teaching IEC 61499 to people from industry and master level
students for more than ten years. The questions and discussion with the stu-
dents has resulted in a much deeper understanding of the standard and how it
should be taught. From this we have learnt that the concepts of IEC 61499
should be introduced in a different order than was originally presented in the
first edition.
xiv Modelling control systems using IEC 61499

Organisation, structure and changes in the second edition
With this second edition, we have incorporated our experience from the last
14 years and restructured the contents as follows:
Firstly, Chapter 1 gives an overview on the domain of industrial automation
systems and their requirements. It aligns IEC 61499 with IEC 61131-3 covering
software concepts such as object orientation and component orientation.
The main models and concepts of IEC 61499 are introduced in Chapter 2. This
is the chapter that has undergone the most changes in order to highlight the inter-
relation of the different models. The concepts of the function block model and its
use in applications has been put to the fore. This is followed by the system model
describing the control hardware and the distribution model, which interlinks
applications with the devices on which they will be executed.
Chapter 3 focuses on the main IEC 61499 function block types, i.e. basic and
composite function block types. The descriptions of the types have been updated to
the latest edition of the standard, common elements such as the interface definition
have been consolidated and the examples have been expanded.
The new Chapter 4 describes means for structuring applications. The descrip-
tion of subapplications has been taken from the original Chapter 3, and adapters
taken from the original Chapter 2. Their descriptions are significantly expanded
and extended with new and reworked examples.
Chapter 5 describes service interface function blocks which provide means for
interacting with services provided by devices or resources. Their description is
aligned to Chapter 3 and a section on communication service interface function
blocks has been added.
Chapter 6 gives an overview on event function blocks and how they can be
used to control event flows in applications. The changes in this section are mainly
corrections, but further examples and use cases of the event function blocks have
also been added.
Chapter 7 shows how the models and concepts of IEC 61499 can be applied to
implement control applications. The concluding Chapter 8 gives an overview on
the current status of IEC 61499, including an outline of the requirements for soft-
ware tools as given in IEC 61499 Part 2. Another addition in the second edition is
an overview on compliance profiles as defined in IEC 61499 Part 4.
Acknowledgements first edition
The development of the IEC function block standard has taken many years invol-
ving numerous meetings, animated discussions, debate and argument. I must,
therefore, thankfully acknowledge all contributions of the members of the IEC 65/
WG6 working group whose efforts are distilled in the IEC 61499 standard. I would
also particularly like to acknowledge the chairman, Dr. Jim Christensen who,
through humour and gentle persuasion, ensured that the working group remained on
track to create a concise and effective standard. I must also thank Jim and Rockwell
Automation for the permission to use his FBDK tool, which I put to good use to
prove the syntax and structure of the PID example given in Appendix D.
Preface xv

I would also like to thank Terry Blevins from Fisher-Rosemount Systems Inc.
for all his information and help on the development of the Fieldbus standards.
Some of his application examples have been particularly useful in demonstrating
how function blocks can be used to model distributed systems.
I would also like to give special thanks to Dr. Bob Brennan at University of
Calgary and Dr. John Wilkinson at Queen’s University Belfast for all their help in
reviewing the manuscript.
Bob Lewis, Worthing, UK, 2001
Acknowledgements second edition
First of all, I’m very grateful to Bob for the opportunity to write this second edition
and his support in developing it. My thanks also go to Jim Christensen as he taught
me the concepts of IEC 61499 back in 2001 and for all the discussions we had since
then.
I would also like to thank the members and students of the Odo Struger Labor
research group at the Automation and Control Institute, Vienna University of
Technology, especially Reinhard Hametner, Ingo Hegny, Martin Melik-Merkumians,
Carolyn Oates, Christoph Sünder and Monika Wenger, for our discussions on how to
implement and apply IEC 61499. In this respect, I would like to thank also the
research partners I had in this time, namely Franz Auinger, Gerhard Ebenhofer and
Thomas Strasser.
I thank Jonathan Burdalo, and Benjamin Brandenbourger and Georg
Neugschwandtner from fortiss GmbH for reading and commenting the manuscript
of the second edition.
Last but not least my thanks go to my wonderful wife Andrea for her patience
in the last months and her comments on many of the figures.
Alois Zoitl, Munich, Germany, 2014
xvi Modelling control systems using IEC 61499

Abbreviations and conventions
ASN. 1 Abstract Syntax Notation One
CPU Central Processing Unit
DCS Distributed Control System
FB Function Block
FBD IEC 1131-3 Function Block Diagram graphical language
FRD Functional Requirements Diagram
GBs GigaBits per second
HMI Human–Machine Interface (see MMI)
HVAC Heating, Ventilation and Air Conditioning
IEC International Electrotechnical Commission
IPMCS Industrial Process Measurement and Control Systems
I/O Inputs and Outputs
IP Internet Protocol
IS International Standard
ISA Instrument Society of America
ISO International Standards Organisation
LD IEC 1131-3 Ladder Diagram graphical language
MBs MegaBits per second
MMI Man–Machine Interface (now replaced by HMI)
MMS Manufacturing Message Specification
OO Object Oriented
OSI Open Systems Interconnection
PAS Publicly Available Specification
PC Personal Computer
PID Three term controller, Proportional, Integral, Derivative closed-loop
control algorithm
P&ID Piping and Instrumentation Diagram
PLC Programmable Logic Controller
POU IEC 1131-3 Program Organisation Unit

SCADA Supervisory, Control and Data Acquisition system
SFC IEC 1131-3 Sequential Function Chart graphical language
SI Service Interface
SIFB Service Interface Function Block
SOA Service Oriented Architecture
ST IEC 1131-3 Structured Text language
TCP Transmission Control Protocol
UDP User Datagram Protocol
UML Unified Modelling Language
XML eXtensible Markup Language
The following font and style is used to distinguish examples of textual program-
ming language from ordinary text:
BEGIN
A := A + 100.5; (* Comment *)
END
This text style is also used to reference textual programming language elements and
also names used in the graphical representation in the text.
The suppression of superfluous detail in textual language examples is indicated
using an ellipsis ‘ . . . ’.
xviii Modelling control systems using IEC 61499

Chapter 1
Introduction
In this introductory chapter we review the background and reasons behind the
development of the IEC 61499 standard. Specifically we will:
● review the design of current day control systems and consider the impact of
new technology,
● look at the reasons for starting the development of the IEC 61499 standard,
● consider the reasons why function blocks are still an important concept to
process and system engineers,
● show how function blocks have some of the characteristics of object- and
component-oriented software,
● show how IEC 61499 models can be used in the control system development
life cycle.
As manufacturing companies fight to compete in today’s unpredictable and ever
changing global markets, there is an increased urgency to improve the agility of
manufacturing systems. To produce competitive and innovative products,
companies must be able to quickly design and create new forms of advanced
automated production. Such levels of automation require the creation of large
systems involving an amalgam of industrial control, manufacturing execution and
business logistics systems. A key characteristic of all of these new systems will be a
built-in ability to rapidly handle change, resulting in agile manufacturing systems
[1]. A manufacturing plant will need to be able to quickly switch product types and
bring new processes on stream to remain in business.
Currently there is growing interest in new technologies and architectures for
creating the next generation of distributed systems for industrial automation. These
will be systems where software is organised as sets of co-operating components
rather than as an integration of large bespoke units of software [2].
Up to now, industrial control systems have been in one of two main camps,
either based on traditional Distributed Control Systems (DCS) or based on Pro-
grammable Logic Controllers (PLCs). Current DCSs, as typically used in petro-
chemical plants and refineries, are structured around a few large central processors,
which provide supervisory control and data acquisition, communicating via local
networks with numerous controllers, instruments, sensors and actuators located out in
the plant (Figure 1.1). A system may have both discrete instruments and out-stations
with clusters of instruments with local controllers. In a DCS, the main supervisory

control comes from one or more central processors. Instruments positioned out in the
plant typically provide local closed loop control, such as for PID1
control.
In contrast, for many machine control and production processes, particular on
automotive production lines, systems have generally been designed using PLCs
(Figure 1.2). In these systems, the Human–Machine Interface (HMI) is normally
provided by a wide variety of different types of panels, lights and switches.
Advanced HMI can also be provided by colour display panels with operator input via
dedicated keypads or from touch sensitive screens. Especially with the introduction
of smart phones and tablet computers this field is currently changing rapidly.
A large PLC system will generally have a number of PLCs communicating via
one or more proprietary high-speed networks. PLCs will typically be connected to a
large number of input and output (I/O) signals for handing sensors and actuators. In
some cases, discrete instruments, for example, for temperature and pressure con-
trol, are also connected to PLCs.
With both design approaches, systems have tended to be developed by writing
large monolithic software packages, which are generally difficult to reuse in
new applications and are notably difficult to integrate with each other. Data and
functionality of one application are not readily available to other applications, even
if the applications are written in the same programming language and running in
the same machine. Significant system development time is concerned with
1
PID – Proportional, Integral and Derivative control algorithm commonly used to provide stable closed
loop control (e.g. for temperature or pressure).
Central supervisory
and control stations
Local network
Distributed instruments
Out-stations with
instrument clusters
Workstation
Figure 1.1 Distributed control system
2 Modelling control systems using IEC 61499

mapping signals between devices and providing drivers to allow different types of
instruments and controllers to communicate.
Both types of system, DCS and PLC, tend to be difficult to modify and extend
and do not provide the high degree of flexibility that is expected in systems for
advanced and flexible automation.
With the emergence of standards in industrial communications such as
Fieldbus, which will allow different types of instruments and control devices to
interoperate, the differences between DCS- and PLC-based systems are starting to
disappear. DCS instruments and PLCs are beginning to offer similar functionality.
Industrial applications are also being implemented on PC hardware with concepts
such as the SoftPLC, i.e. PLC logic running on a normal PC. As industrially har-
dened PC (IPC) platforms that offer high reliability become more common, we will
see a trend to using more PC-based controllers. Until recently, classical PLCs could
only be programmed using proprietary languages as offered by the PLC vendor.
With users now requesting a more open approach to software, a new breed of soft-
controller is emerging that can be programmed in a wide range of different pro-
gramming languages. This new breed of soft-controllers is often referred to by the
term Programmable Automation Controller (PAC).
We can now foresee the time when systems for controlling industrial, manu-
facturing and business processes start to merge. For example, a company can
seamlessly link a business system running in a head office to manufacturing
PLC network
HMI display
PLC with
discrete
instruments
Figure 1.2 PLC control system
Introduction 3

processes and industrial control systems or even controllers running in any plant in
any part of the world.
Figure 1.3 depicts part of a system having advanced distributed functionality.
In such systems, each device connected to the industrial network can provide part
of the control functionality. Smart devices, such as pumps, valves, or sensors will
have built-in control functionality that can be linked by software with more intel-
ligent devices such as HMI panels, temperature controllers and soft-controllers to
form the total control system functionality. For example, a pressure sensor can be
linked directly by software to a valve actuator and to a display bar graph on an HMI
panel. A slider on an HMI panel can be directly software wired to the set-point of a
PID controller controlling the speed of a pump.
To achieve these high levels of integration and yet enable the creation of
flexible systems that can be re-engineered as industrial and business needs change,
a completely new approach to software design will be required – a new technology
based on the interaction of distributed objects [3]. There are several software
technologies already well advanced that are set to have an influence in this area.
The first have been middleware technologies like CORBA2
[3] or DDS3
[4] from
the Object Management Group (OMG). A further decoupling was achieved by
introducing Service-Oriented Architectures (SOA), where components offering
services can be flexibly combined using these services [5]. On top of these tech-
nologies, several coordination technologies have been presented, e.g. Complex
Event Systems [6] or the Enterprise Service Bus concept [7].
In the domain of industrial process measurement and control systems, the
technologies from the OPC Foundation allow seamless data access regardless where
they are located, be it in a remote industrial controller in a blast furnace or in the PC
2
Common Object Request Broker Architecture.
3
Data Distribution Service.
Temperature
controller
Pump Valve actuator
Local network
Pressure
sensor
Position
sensor
Human–machine
interface
Soft controller
Figure 1.3 Advanced distributed functionality

of the production manager’s office [8]. Internet technologies using Ethernet, peer-to-
peer communication or SOA are also being considered for manufacturing systems.
With the new OPC Unified Architecture [9], there are proposals to bring this seamless
interoperability also into small industrial devices (e.g. sensors and actuators).
The industrial community has long been aware that the ready interconnection of
software components, such as in the form of function blocks, will have major
advantages especially for end-users. These advantages will include improved software
productivity through reuse of standard solutions, improve design flexibility by being
able to plug-and-play software and devices from different vendors. So far, the new
standards all enable ‘technical integration’ of distributed components, but the next
major hurdle is ‘semantic integration’ (i.e. define a meaning behind the data). We may
be able to link and exchange data between software in a remote industrial controller to
a control algorithm running in a PC, but will the connection be meaningful?
1.1 IEC 61499 function block standard
The International Electrotechnical Commission (IEC) has developed a specific
standard IEC 61499 [10] that defines how function blocks can be used in dis-
tributed industrial process, measurement and control systems. This work may help
solve part of the semantic integration problem.
In industrial systems, function blocks are an established concept for defining
robust, reusable software components. A function block can provide a software
solution to a small problem, such as the control of a valve, or control a major unit of a
plant, such as a complete production line. Function blocks allow industrial algorithms
to be encapsulated in a form that can be readily understood and applied by people who
are not software specialists. Each function block has a defined set of input data, which
are read by the internal algorithm when it executes. The results from the algorithm are
written to the function block’s outputs. Complete applications can be built from net-
works of function blocks formed by interconnecting function block inputs and outputs.
The IEC 61499 standard, which builds on function block concepts defined in
the PLC language standard IEC 61131-3 [11, 12], was developed in liaison with
Fieldbus standardisation work. It is envisioned that the Application Layer part of
the Fieldbus communications stack will provide the software interface to allow
remote function blocks to interoperate over Fieldbus. However, IEC 61499 was
developed as a generic standard that is also applicable in other industrial sectors –
in fact, wherever there is a requirement for software components that behave as
function blocks, for example in building management systems.
IEC 61499 defines a general model and methodology for describing function
blocks in a format that is independent of implementation. The methodology can
be used by system designers to construct distributed control systems. It allows a
system to be defined in terms of logically connected function blocks that run on
different processing resources.
Figure 1.4 depicts how the IEC 61499 methodology could be used as part of
the system design life cycle. The design of a control system typically starts with the
Introduction 5

analysis of the physical plant diagrams and documentation on the control system
requirements. This analysis leads to the phase of defining areas of functionality and
their interaction with the plant. The final phase results in mapping functionality into
physical resources such as PLCs, instruments and controllers.
The use of IEC 61499 can be best demonstrated by considering the following
phases in the design of a distributed control:
● Functional design phase: During this phase, process engineers analyse the
physical plant design, for example using Piping and Instrumentation Diagrams
(P&ID), to create the top-level functional requirements. These can be repre-
sented as a series of blocks that outline the main software components and their
primary interconnections. At this design phase, the physical distribution of
the software blocks is not considered. In many cases diagrams that show the
physical design of the plant or machinery, such as P&IDs, also show the
location of active devices such as valves and pumps and instrumentation
points, such as the location of pressure and temperature sensors.
● Functional distribution phase: In a distributed system, a further design phase is
required to define the distribution of control functionality onto processing
resources. IEC 61499 standard provides models and concepts for defining the
distribution of functionality into interconnected function blocks. System
engineers complete the detailed design by mapping the software requirements
onto IEC 61499 function blocks. These may be distributed on various pro-
cessing resources. In many cases, function blocks as provided in field devices
will be exploited; for example intelligent devices such as smart valves may
provide software packaged as a function block.
Physical system
Design
Implementation
Physical plant and
instrumentation design e.g.
Piping and Instrumentation
Diagram (P&ID)
Top level Functional
Requirements Diagram
(FRD)
Distributed Function Block
Diagram (IEC 61499)
081 PT
Tank 2
Tank 1
082 PT
Figure 1.4 Applying IEC 61499

Each function block in turn will have its own particular software design life
cycle. Some function blocks will need to be specifically designed for a system
application, in other cases, existing function blocks within instrumentation and
controllers can be used.
We will see later that the function block model defined by IEC 61499 provides
just a subset of the views in a distributed system design. Other design views will be
necessary to give all aspects of a system design. IEC 61499 is the first step in
providing design methodologies for developing and modelling distributed
applications.
As the trend to use component-based software continues, it is foreseen that
industrial controllers and instruments will either provide function blocks as part of
the device’s firmware or provide function block libraries from which function
blocks can be selected and downloaded. System design will become the process of
software component selection, configuration and interconnection, just as much of
electronic hardware design is now primarily concerned with the selection and
interconnection of integrated circuits (chips).
IEC 61499 allows function blocks that encapsulate software functionality and
algorithms to be defined in a standard format. This allows tools and other standards
that deal with function blocks to use the same concepts and methodology. The IEC
61499 standard also defines a range of communication function blocks, such as
Client/Server function blocks, which can be used to formalise the exchange of data
between function blocks in different physical processing resources. There are also
service interface function blocks to provide interfaces with the processing resource
infrastructure.
Figure 1.5 shows three interconnected function blocks, representing the con-
nections between a pressure transmitter and PID control function block and a pump
using concepts from the IEC 61499. Notice that there are both data and event flows
between function blocks. We will see later that the IEC 61499 methodology allows
data and its associated event to be closely coupled, that is, to be coherent or
alternatively for events and data to be handled asynchronously.
Event flow
Data flow
Figure 1.5 Function block data and event flows
Introduction 7

Figure 1.6 depicts the trends in industrial control technology during the last
50 years; since the 1950s, there has been a steady growth in the functionality pro-
vided by control systems due to advances in both hardware and software. As control
systems became digital, using microprocessors, there has been an increased need for
standards to reduce unnecessary diversity in software and lessen cross-system inte-
gration problems.
IEC 61131-3 has focused on standardising PLC languages for single processors
or small configurations with a few closely coupled multiprocessors. With the move to
large scale distributed functionality, there is a need for further standards such as IEC
61499 to harmonise the way functionality is defined and distributed. There is also a
growing requirement that all the related system build tools can be integrated as well.
For example, all the software tools used to design, configure and manage a
distributed system should run as an integrated suite. The design tool that defines a
system should be integrated with tools for programming and configuring devices
along with tools for defining HMI screens and configuring industrial networks. It is
the intention that IEC 61499 will define system models that will help not only with
the design of functionality in distributed systems but also with the integration of
system tools through the definition of data and information models.
1.2 Development of function block concept beyond
IEC 61131-3
Why was it not possible to use the function block concepts defined in IEC 61131-3
for distributed systems? There are a number of limitations with the original func-
tion block concept introduced by the PLC Languages Standard IEC 61131-3. With
the IEC 61131-3 Function Block Diagram (FBD) graphical language, function
Mechanical
function
Analogue
device
Transistor Microprocessor
Industrial
communications
Data
modelling
Object-oriented
technology
Advancing technology
Distributable
interoperable
components
Digital
device
Function
distribution
Tool
integration
IEC 61499
IEC 61131-3
Functionality
Figure 1.6 Development of technologies for industrial control

blocks can be linked by simply connecting data flow connections between function
block input and output variables, see Figure 1.7a. Each function block provides a
single internal algorithm that is executed when the function block is invoked. The
normal execution order is determined by the function blocks dependency on the
other function blocks; the order normally runs from left to right because function
blocks to the right depend on the output values of function blocks on the left.
However, when a feedback path is introduced, as shown in Figure 1.7b, the
execution order cannot be determined from the diagram, since the execution of both
function blocks depends on an output value of the other function block. In a com-
plex network, it is very difficult for a programming system to determine a valid
order of execution. To overcome this problem, many IEC 61131-3 programming
systems provide additional mechanisms to define the execution order of function
blocks. For example, the user can view a list of function blocks and manually
assign an execution order. Unfortunately, such mechanisms are outside the scope of
the IEC 61131-3 standard. As a consequence, an important aspect of a function
block network is that the method for defining the execution order of function blocks
is not consistent or portable across different control systems.
There is one feature in IEC 61131-3 that does provide a crude mechanism for
passing execution flow through a chain of function blocks that is worth consider-
ing: the use of the EN input and ENO output signals (Figure 1.8). The EN and ENO
(b) Network with feedback connection
(a) Function block network
Figure 1.7 Using IEC 61131-3 function blocks
Figure 1.8 Execution control using IEC 61131-3 EN and ENO
Introduction 9

signals were intended for function blocks to pass ‘power flow’ when used in rungs
of a Ladder Diagram (Figure 1.8). However, it is now recognised that the EN and
ENO do not provide the degree of flexibility needed for complex function block
networks. In effect, the EN and ENO signals can be regarded as a means to pass
events between function blocks. EN signals that the function block may be invoked
because its input data is ready; ENO is signalling that the function block has exe-
cuted and the output data is ready for the next function block. We will see that this
idea of event passing has been extended in IEC 61499.
The focus of the IEC 61131-3 standard has been to define a software model
and languages for PLCs where software is typically running on one or a few tightly
coupled processing resources. Therefore, the IEC 61131-3 software model, see
Figure 1.9, does consider configurations that have multiple resources. The standard
provides two different mechanisms for passing data and control signal between
resources, namely global variables and communications function blocks.
1.2.1 Global variables
Using global variables located at the configuration level, it is possible to transfer
data and control signals between programs and function blocks running in different
resources. However, it is well understood that the use of global variables is a very
poor and sometimes unsafe mechanism for handling data transfer between proce-
dures running in different processors. It is not possible to clearly identify where
global variables are updated and where they are used. There is no graphical means
Configuration
Resource Resource
Task
Program Program Program Program
FB
Global and directly represented variables
Access paths
Communication functions
(defined in IEC 61131-5)
Key
FB
Variables
Function Blocks
Access paths
Execution
control path
FB FB FB
Task Task Task
Figure 1.9 IEC 61131-3 software model

in IEC 61131-3 to define the linkage between global variables and the variables
referencing them, that are located inside programs and function blocks. There are
also more serious problems with global variables because the timing and syn-
chronisation of signals passed by global variables is difficult to define. Further-
more, the mechanism provided within the configuration for handling the
initialisation and updating shared global variables are not defined in IEC 61131-3.
1.2.2 Communications function blocks
Part 5 of the PLC standard, IEC 61131-5 [13], is concerned with communications
services for PLCs programmed using the IEC 61131-3 software model. IEC 61131-5
defines a range of function blocks that can be used to exchange data between PLCs.
This includes function blocks to allow a PLC to function as a ‘server’, i.e. allow a
PLC to support and respond to external service requests. There are also function
blocks to support ‘client’ behaviour i.e. support services that enable a PLC to
request and control another PLC or system functioning as a server.
IEC 61131-3 allows a subset of variables within a configuration to be accessed
externally. These are called ACCESS variables and can be accessed via a com-
munications interface from an external PLC using communication function blocks
or can be accessed from other non IEC 61131-3 devices using services that are
outside the IEC 61131-3 standard.
We have seen that IEC 61131-3, along with the manufacturing messaging stan-
dard IEC 61131-5, provides a range of different software mechanisms for allowing
PLCs to communicate. These are quite adequate for systems with only a few PLCs.
However, it was clear to the IEC working group developing the function block
standard that the IEC 61131 communications model has serious limitations. Concepts
such as global variables and communications function blocks do not provide a clear
and concise method for defining the connections between distributed function blocks.
A consistent communications model was required that could be used not only
for PLC to PLC communications but also between devices large and small dis-
tributed over industrial networks. The new function block model had to be scalable
and extensible – so that it would be equally applicable to modelling the commu-
nications between control systems, PLCs and controllers as between smaller
Fieldbus devices, such as smart valves and sensors. In fact, a function block model
was sought that would cover all types of devices and controllers.
To summarise, the main deficiencies of the software model provided by IEC
61131-3 for distributed systems are as follows:
● Applications in the IEC 61131-3 model are not distributable over multiple
resources.
● The function block execution order is not always clearly defined and not under
the direct control of the application developer.
● The assignment of tasks to programs and function blocks does not provide
sufficient flexibility.
● The ‘scanned’ nature of IEC 61131-3 function block execution cannot be
mapped to function blocks connected across distributed resources.
Introduction 11

1.3 Development of IEC 61499
When the International Electrotechnical Commission first identified the need for a
new function block standard for distributed industrial process measurement and
control systems in 1990, it was realised that these function blocks would be a
generic concept that could be applied to a wide range of standards. For example,
function blocks concepts can be used within PLCs, smart devices, building man-
agement systems and Fieldbus protocols. At that time there was already a standard
utilising a function block concept under development, namely IEC 61131-3
focusing on the harmonisation of PLC programming languages. In order to
leverage the existing know-how, the IEC technical committee TC 65 assigned the
work on IEC 61499 to the same working group (at that time WG 6). The IEC
working group for IEC 61499 has members from the United States, Japan, the
United Kingdom and many European countries, who represent both industrial
control system suppliers and end-users.
IEC 61499 is a multi-part standard that took a number of years to complete.
The IEC standardisation process is managed in four main phases: (i) the standard
development phase, (ii) the Publicly Available Specification (PAS) phase, (iii) the
final review and publishing phase and finally (iv) the maintenance and republ-
ishing phase. The last phase is performed every 5 years. PAS is a concept being
promoted by the IEC for publishing standards early, avoiding some of the more
time-consuming bureaucratic stages of standards approval. A PAS can be pub-
lished even though the standard has not completed all the international standar-
disation approval processes. A PAS can be regarded as a trial standard that is made
available to the industrial community to allow the early development of products
and services.
For the first part of IEC 61499, the PAS phase started in 2000 and resulted in
the final publication of all parts as an international standard in 2005. Feedback
gathered during the PAS phase resulted in several changes and improvements
making IEC 61499 easier to implement and apply. In 2010 the first maintenance
was performed. During this first maintenance phase, several issues and ambiguities,
which had been identified since the publication of the first edition were corrected.
The resulting second edition of IEC 61499 was published in 2012. The second
edition is also the basis of this book and consists of three parts: 1, 2 and 44
.
Part 1 covers the architecture and concepts for designing and modelling distributed
function block–oriented systems and covers the following topics:
1. General requirements, including an introduction, scope and normative refer-
ences (i.e. to other standards), definitions and reference models.
2. Rules for the declaration of function block types, and rules for the behaviour of
instances of function block types.
4
Part 3 has been withdrawn in 2008 (see Section 8.1 for more details).

3. Rules for the use of function blocks in the configuration of distributed indus-
trial process measurement and control systems (IPMCS).
4. Rules for the use of function blocks in meeting the communication require-
ments of distributed IPMCS.
5. Rules for the use of function blocks in the management of applications,
resources and devices in distributed IPMCS.
The main focus of this book concerns the architecture and models defined in Part 1
of the IEC 61499 standard.
Part 2 of the IEC 61499 standard [14] addresses the definition of formal infor-
mation models that will enable CASE5
tools and utilities to manipulate and
exchange system designs based on function blocks. The main focus of Part 2 is the
‘engineering task support’ and it provides guidance on engineering tasks concerned
with the design, implementation, operation and maintenance of IPMCS constructed
using the architecture and concepts defined in Part 1.
Originally the STandard for the Exchange of Product data, STEP (ISO 10303),
has been considered as the means by which function block designs are saved and
exchanged across different design workstations. STEP is used by CAD stations for
storage and exchanging of electronic circuit designs in an implementation inde-
pendent form. There is clearly a strong synergy between electronic schematics and
control system designs based on function blocks.
However, finally the eXtensible Markup Language (XML) has been selected in
IEC 61499 Part 2 as a means to save and exchange function block definitions. This
provides the exciting possibility of being able to transfer designs across the Internet
and view them using Web browsers. XML has been developed as major enhance-
ment to the Hypertext Markup Language (HTML) currently used for Web page
creation. Using XML will allow designs to be saved with various attributes
including version information and graphical layout details – this is discussed fur-
ther in Section 2.6.
Part 4 [15] targets the important topic of how compliance to IEC 61499 is defined
and how vendors need to specify it. Already very early in the development com-
pliance was identified as a very important consideration particularly with dis-
tributed systems where devices from different vendors are used in a system. On the
other hand (as stated) IEC 61499 is generic and therefore does not define a concrete
implementation of a distributed IPMCS in all details. In order to address this issue,
Part 4 of IEC 61499 defines rules for structuring and developing compliance pro-
files. A compliance profile as defined in IEC 61499 Part 4 needs to specify the
implementation of the features of IEC 61499 Part 1 and Part 2 considering the
important properties of distributed IPMCS:
● Interoperability provisions define which means are used allowing devices from
multiple vendors to interact via communication systems.
5
CASE – Computer Aided Software Engineering.
Introduction 13

● Portability provisions define an exchange format for IEC 61499 entities
(e.g. function blocks, applications, system configurations) allowing software
tools from multiple vendors to produce, parse and interpret them correctly.
● Configurability provisions define means that allow software tools from
multiple vendors to configure devices from multiple vendors.
It was the original intention of the IEC that the new function block standard
would become a generic standard that could be used as a basis for standards
throughout the domain of industrial process measurement and control. For this
reason, because of its generic nature, IEC 61499 appears to be a rather academic
standard. It has been deliberately defined to be ‘application domain neutral’, i.e. it
contains no specific features for any particular industrial application area. It is
designed so that other standards can build on the IEC 61499 concepts and add their
own domain specific extensions.
A good example of a standard built on the IEC 61499 function block model is
demonstrated by the Process Control Function Block working group. This group has
the primary objective of defining function blocks for use in the process industries,
but they have taken concepts from the generic function block model in IEC 61499 as
the basis of their work. By applying the generic model to real industrial process
control applications, the process control group has provided useful feedback to the
IEC 61499 working group. In many cases they have highlighted shortcomings in the
function block model that have resulted in improvements to IEC 61499.
Furthermore, during the evaluation phase of the standard, it was found that the
function block models as defined in IEC 61499 had great potential for improving
system design. In the past few years several platforms (i.e. engineering tools and
control devices) implementing the concepts of IEC 61499 have become available.
These allow the development and operation of distributed IPMCS directly using the
models of IEC 61499.
1.4 Why use function blocks
To many software engineers, the idea of function blocks seems to some degree
archaic – a strange software paradigm that appears to represent software as pieces
of hardware. In effect, that is exactly what a function block is, a model of software
that treats the encapsulated behaviour in a form that is similar to an electronic
circuit. However, in improving the software development process, the key aspect
has always been to add further abstractions and higher level software modelling
aspects in order to cope with an increased complexity.
Objects, used in the Object-Oriented (OO) software world which are in some
respect similar to function blocks, have become successful because they can be
used to model the behaviour of entities and concepts in the real world. The main
benefits from using objects can be summarised as:
Objects reflect the real world: When designing an application, it is more
natural and intuitive to represent real-world entities associated with an
application as objects, e.g. document, employee, and product.

Objects are stable: Generally, objects are proven software elements that do not
change significantly. In many cases, developers use the same object classes
in a wide range of applications. For example, when an object is created that
represents all the behaviour and characteristics of an entity such as ‘product
supplier’, it can be used in a wide range of different business applications
dealing with suppliers. A ‘product supplier’ object would typically have
details such as name, address, product ranges, trading terms etc., and
methods to obtain and update this information.
Objects reduce complexity: A developer can work with an object without really
understanding how the object works internally. An application can be
developed by creating and linking objects – there is generally no need to
understand the object’s internals.
Objects are reusable: Once an object is developed and tested it can become
part of a developer’s repertoire. In some cases, an object can be published in
a library, where it can be used by developers either locally or even globally.
While OO software development greatly changed the world of software
development, it could not keep up with the promise of providing extensible reu-
sable software. It has been shown that objects are very often designed to be too
specific for their use-case or depend on the context in which they are used, limiting
their general applicability [16].
In order to improve this situation the stronger concept of software components
has been introduced by Szyperski [17]. He defines a software component similar to
an object: ‘‘A software component is a unit of composition with contractually
specified interface and explicit context dependencies only. A software component
can be deployed independently and is subject to composition by third parties.’’ [17,
Section 4.1.5]. Software components have the following main properties:
● Unit of independent deployment: This property requires that a component is
self-contained and is clearly separated from the environment and other com-
ponents. A component will never be deployed partially.
● Unit of third-party composition: Third parties who have no information on the
internal construction of components can use them in combination with other
components.
● Component interaction only via explicit interfaces: In order to provide the first
two properties the interaction with components has to occur via clearly defined
interfaces. A purely static interface definition (e.g. method signature) is not
enough; dynamic interface definitions on how to correctly use it are also
required. Furthermore, components must not have hidden interfaces (e.g. glo-
bal variables).
As in component-oriented software development, in the function block world,
the system designer’s main focus is to take standard, proven encapsulated func-
tionality and link it together in the quickest and most intuitive way possible. The use
of function blocks is nearer to the mind-set of the industrial system designer who is
familiar with connecting physical devices together in different ways to provide a
particular system solution. Function blocks also share most of the characteristics of
Introduction 15

software components, which results in some significant benefits to the system
developer and end-user:
● The quantity of control software to be developed for an application is reduced
by using function blocks.
● The time required to develop control systems is reduced.
● Control systems using the same types of function block will have more
consistent behaviour.
● The quality of control systems will be improved.
The current trend in software development is to use abstract formal models for
describing software at an even higher level [18]. Especially by using domain
specific modelling approaches certain software systems can be developed by
domain experts with less effort at higher quality. As we will see in the following
chapters, IEC 61499 provides both an effective means for software modelling and a
comprehensive modelling language that addresses the design of distributed control
systems, notably in the IPMCS domain.
1.5 System design views
The design of software for any large project can be very complex. Especially where
there is also some aspect of distributed control involving software running in dif-
ferent processing resources, the design problems can be daunting. There is a clear
requirement for a number of graphical design views to allow the different aspects of
a design to be analysed and expressed. Some views will express the abstract aspects
of the design, while others are required to show the physical structure of the system
or the way the software is organised.
No matter how hard people have tried, it is just not possible to convey all
aspects of a system design using one design methodology. There are so many
design issues to consider that they cannot be expressed in a single type of graphical
notation, such as:
● What is the top-level software structure?
● What functionality does the system deliver to its end-users?
● How is the functionality distributed throughout the system?
● How are the system components connected?
● How are the software libraries and standard components managed?
● How does the system respond to certain critical events?
Many system design problems are a result from trying to use too few or inappropriate
different design methodologies to depict all the aspects of a system design.
A particular design view might be able to show how software for a system is
logically connected, but it would not be able to depict the way the system responds
to events.
In fact, it is now recognised that most complex software designs can require
at least four different design views and a set of scenarios – this forms an

architecture known as the 4 þ 1 View Model, as proposed by Kruchten [19]
(Figure 1.10).
Although Kruchten has considered applying these design views to the world of
object oriented software, the same design views are also applicable to distributed
control system design.
1.5.1 Logical view
This design view is used to depict the functional requirements of the system.
It expresses the software functionality as required by the system user. In a dis-
tributed system design, it would show the main software function blocks and the
main interfaces between them. Issues such as how the system functionality is
distributed and executed are not addressed.
A methodology such as the IEC 61499 applications as well as the function
block model itself can be used to define some aspects of the logical design view.
1.5.2 Process view
The process design view is concerned with many of the non-functional require-
ments of a system; these include performance, system distribution and issues such
as concurrency. Kruchten defines the process view as depicting ‘logical networks
of communicating programs that are distributed across a set of hardware
resources’.
Distribution of functionality
showing ‘threads of control’ –
IEC 61499 function block diagram
System topology, network
layout, devices, controllers –
IEC 61499 system model
System user
functionality
System software management,
e.g. function block libraries
Logical view Development view
Physical view
Process view
Scenarios
Figure 1.10 The 4 þ 1 View Model of system development
Introduction 17

This corresponds almost exactly to the concepts in the IEC 61499 Function
Block standard, which provides an architecture for depicting the implementation
view of a distributed system as networks of interconnected function blocks.
1.5.3 Development view
The development view depicts how the software that is used to build a large system
is organised. Building a large distributed control system will involve numerous
software libraries and software modules. The development view shows the rela-
tionships between software components, such as function blocks in terms of ease
of reuse, constraints, component size and version compatibility. For example,
consider a function block used for conveyor control, where we would want to
indicate which device types support it and we would like to show any constraints on
other function blocks that need to interact with it.
Currently there is no IEC standard methodology that deals with the develop-
ment view of a distributed control system. With the interface concept provided by
the adapter model, in IEC 61499 only the limited aspect of the provided and
required interaction points can be defined.
1.5.4 Physical view
In a distributed control system, the physical view is well understood. It depicts the
physical devices and controllers in a system and shows the various network com-
munications links between them. A physical view will generally consider the
physical configuration of the system showing the location of devices and details on
bus and communications links.
This corresponds partly with how IEC 61499 specifies the system model,
which provides means to model available devices, communication links and the
interconnection of the devices. Physical placement in the plant as well as interac-
tion with the process is not considered.
1.5.5 Scenarios
The last but important design view that completes any system design is what
Kruchten calls scenarios. A scenario depicts the major interactions between units
of software to provide the most important, key functionality of a system.
For example, in a distributed control system, some important scenarios to consider
might be system start-up, device fault detection and recovery, recipe activation
and system shutdown. Each scenario would consider the interactions between the
different functional parts of the software. A scenario might show both aspects of
the logical and process design views.
By describing the various scenarios, the designer can review and test the
design by asking a series of ‘what if?’ questions. The design cannot be considered
to be complete until all the key scenarios have been defined. There is currently no
methodology defined by any IEC standard that can be used to define scenarios for
distributed control systems.

From this quick overview of the 4 þ 1 View Model of Architecture, it is clear
that IEC 61499 provides at least in parts three of the five design views required for
distributed control systems. However, IEC 61499 does represent an important step
towards a unified design architecture. The other views will no doubt emerge as
designers start to face the challenge of building large distributed systems.
1.6 The future beyond IEC 61499
The function block model proposed by IEC 61499 has been criticised for not
adopting concepts from OO software technology as has been done with the latest
revision of IEC 61131-3. However, in addition to OO software technologies,
especially higher level concepts like programming in the large and extended
software modelling concepts would be needed. The standard has started by mod-
elling existing industrial function block concepts but extensions to move towards
these concepts will undoubtedly need to be considered in the near future.
New industrial standards for communications and software components will
clearly bring benefits in allowing physical devices and software to be readily
interconnected. However, before we can achieve truly interoperable software
components that can be used to implement large systems, we need to agree on
general methods for describing requirements such as information models and data
transformations. It is the intention that IEC 61499 should be able to address this
problem in the domain of industrial control systems.
In the following chapters we will review the concepts from IEC 61499 and see
how this standard can be used to model the design of distributed control systems.
Introduction 19

Chapter 2
IEC 61499 models and concepts
We will now review the main models and concepts defined in IEC 61499 to gain a
general overview of the function block standard. It is advisable to have some
understanding of the material in this chapter before proceeding into any of
the following chapters where we will review specific features of IEC 61499 in more
detail.
Topics covered in this chapter include:
● characteristics of function blocks and their execution,
● the different forms of function blocks,
● service interface function blocks to provide interfaces into hardware and
operating systems,
● models to represent applications independent from the system configuration,
● the system, device and resource models for distributed control systems,
● the distribution model which assigns applications to the devices and resources,
● exchange and storage formats for IEC 61499 entities.
Before we proceed to look at the many models and concepts introduced by IEC
61499 in detail, let us reconsider the scope of the IEC 61499 standard as first
discussed in the introductory chapter. Surprisingly the primary purpose of IEC
61499 is not as a programming methodology but as an architecture and model for
distributed systems. IEC 61499 provides a set of models for describing the beha-
viour and structure of distributed industrial process measurement and control
systems using the function block concept. This is an important distinction and must
be understood to avoid many of the misunderstandings that exist about IEC 61499.
IEC 61499 provides terminology, models and concepts to allow the imple-
mentation of a function block oriented distributed control system to be described in
an unambiguous and formal manner. Having a formal and standard approach to
describing systems will allow systems to be validated, compared and understood.
This is the first step towards standard programming methodologies for distributed
systems. The IEC 61499 standard writers have taken the view that it is not possible
to have a consistent programming methodology unless there is a consistent archi-
tecture that underpins what we are trying to program.
We will now review the various models introduced by IEC 61499 that together
form the architecture for a function block oriented distributed industrial process
measurement and control system.

2.1 Function block model
At the core of the standard is the function block model that underpins the whole IEC
61499 architecture. A function block is described as a ‘functional unit of software’
that has its own data structure which can be manipulated by one or more algorithms.
A function block type definition provides a formal description of the data structure
and the algorithms to be applied to the data that exists within the various instances.
This is not a new concept but based on common industrial practice applied
to reusable control function blocks of various forms. A good example is the Pro-
portional, Integral and Derivative (PID) function block used in many PLCs and
controllers. The system vendor will typically supply a type definition for a
PID function block. The programmer can then create multiple instances of the PID
function block within the control program, each of which can be run independently.
Each PID instance, such as ‘Loop1’, ‘Loop2’ will have its own set of initialisation
parameters and internal state variables and yet share the same update algorithm.
2.1.1 General characteristics
IEC 61499 defines several forms of function blocks, which we will review in detail
in later chapters. The main features of an IEC 61499 function block are summarised
as follows:
● Each function block has a type name and an instance name. These should
always be shown when the function block is depicted graphically.
● Each function block can have event inputs, which can receive events from
other function blocks via event connections.
● Each function block can have event outputs, which can be used to propagate
events on to other function blocks.
● Each function block can have data inputs that allow data values to be passed in
from other function blocks.
● Each function block can have data outputs to pass data values produced within
the function block out to other function blocks.
● Events can be associated to data using the WITH qualifier. In the graphical
representation this is shown using a small square connector that links the event
with its associated data. For inputs and outputs the meaning is as follows:
* On the occurrence of an input event its associated input variables are
updated (i.e. sampled from the connection), other input variables retain
their values (i.e. are unchanged).
* On the triggering of event outputs the associated data outputs will be made
available (e.g. sampled onto the connection), other outputs stay unchanged.
● The IEC 61131-3 data types are utilised for the variables’ data types
(see Appendix A for an overview on available data types).
● Function blocks encapsulate functionality which may contain internal variables.
The kind and form of the encapsulated functionality depends on the function
block type.

● As IEC 61499 does not allow global variables, the encapsulated functionality
only has access to function block input, output and internal variables.
● All function block data (i.e. input, output and internal) is retained between
function block invocations.
In Figure 2.1, the main characteristics of an IEC 61499 function block are depicted.
The top part of the function block, called the ‘Execution Control’ portion, contains
a definition to map events on to encapsulated functionality. That is, it defines which
encapsulated functionality defined in the lower body is triggered on the arrival
of events at the ‘Execution Control’ and when output events are triggered – what
the standard calls the ‘causal relationship among event inputs, event outputs and the
execution of encapsulated functionality’. The standard defines means to map the
relationships between events arriving at the event inputs, the execution of encap-
sulated functionality and the triggering of output events depending on the type of
function block – this will be discussed in later chapters on the different function
block types.
The lower portion of the function block contains the encapsulated functionality
with possible internal data – both of which are hidden within the function block.
A function block is a type of software component and, if well designed, there should
be no requirement for a user to have a detailed understanding of its internal design.
A function block relies on the support of its containing resource to provide
facilities to schedule encapsulated functionality and map requests to communica-
tions and process interfaces.
Resource capabilities
(scheduling, communications and
process mapping)
Event inputs
Event flow
Data flow
Data inputs Data outputs
Data flow
Event flow
Event outputs
Execution control
(hidden within block)
Encapsulated
functionality
Figure 2.1 Function block characteristics
IEC 61499 models and concepts 23

The standard states that a resource may optionally provide additional features
to allow the internals of a function block to be accessed. Clearly, say, in a Fieldbus
device, it would be always useful for maintenance or commissioning purposes to be
able to examine the internal variables within a function block. So there may be
‘back-door’ methods to access function block internals; however, from the IEC
61499 architecture view point, control variables and events are only passed by the
external exposed interfaces.
Note: IEC 61499 function blocks contain all algorithms and initialisation
values to define their complete behaviour.
2.1.2 Execution model for function blocks
The execution model generally defines function blocks as passive elements. They
require a trigger by an input event in order to invoke its encapsulated functionality.
The execution order is best described with the aid of Figure 2.2. The numbered
features on the function block show the order in which the different parts of the
function block are executed. The model assumes that the execution environment1
in
which a function block exists provides a scheduling function that ensures that each
phase of function block execution occurs in the correct order and at the correct
priority. Furthermore the standard defines the execution of a function block as
algorithmic. That means that it terminates in a finite time. Therefore, blocking
elements may not be used within a function block. For real-time constrained
applications the execution time constraints can be stronger (i.e. below an applica-
tion specific threshold).
There are a number of discrete phases, each of which may take some period of
time to elapse, required for the function block to execute; each phase depends on
1
In standard terminology a resource, see Section 2.3.2.
Execution control
Encapsulated
functionality
3 4 6 7
5
1
2 8
Scheduling function
Figure 2.2 Execution model for function block

defined interactions between the function block and the underlying scheduling
function. Figure 2.2 depicts the eight steps that must occur sequentially for the
function block to operate; the termination of each phase is defined by a particular
numbered step.
1 Data values coming from other function blocks are made available at the
function block data inputs.
2 An input event arrives resulting in the sampling of the associated input vari-
ables (i.e. WITH qualifier) and in the notification of the execution control.
3 Based on the function block’s current state the execution control signals the
scheduling function that a certain element of its encapsulated functionality is
ready to execute.
4 After some period of time as determined by the loading and performance
characteristics of the resource, the scheduling function starts to execute the
requested function block’s encapsulated functionality.
5 The encapsulated functionality performs its task, processes input values and,
in some cases, also processes internally stored values to create new output
values that are written to the function block’s outputs.
6 The encapsulated functionality completes its execution, and signals this to the
scheduling function to indicate that updated output values are stable and ready.
7 The scheduling function invokes the function block’s execution control,
notifying it about the finished execution of the encapsulated functionality and
enabling it to generate an output event. Different output events (or also none)
may be generated depending on which input events have arrived and the
internal state of the execution control.
8 The execution control in turn creates an appropriate output event at the
function block’s output event interface, and associated output variables are
made available to the connected function blocks (e.g. sampled onto the con-
nection). The output event is used to trigger the execution of downstream
function blocks, signalling that they can now use output values generated by
this function block.
Note: After the input variable sampling in step 2 , the input variables are not
changing during the whole function block execution triggered by an input event
occurrence. This ensures stable and deterministic data values during the execution
of encapsulated functionality.
The presented sequence of execution steps is the most basic execution
sequence that occurs as a result of an input event arrival. Depending on which input
events have arrived and the internal state of the execution control the steps 3 – 8
can be taken several times. In such cases several output events may be sent in
response to the triggering of one input event.
It is important to note that there are a number of constraints on this execution
model. These timing phases cannot overlap and must occur in the prescribed order
for the function block to execute correctly. However, in some implementations,
some phases can be so short in duration as to be regarded as being instantaneous.
IEC 61499 does not define limits on any of these times. However, it does state that
IEC 61499 models and concepts 25

in any function block model it should be possible to define the duration of these
different phases in order to accurately model the timing characteristics of the
complete function block network.
The standard defines the following durations that will be significant when
building applications:
Tsetup ¼ T 2 T 1 Time between the availability of input values (i.e. updated
by preceding function blocks) and the arrival of an input
event triggering their processing.
Tstart ¼ T 4 T 2 Time between receiving an input event and executing the
function block’s encapsulated functionality. This dura-
tion may depend on the resource loading, i.e. how many
other function blocks are also in the scheduling func-
tion’s pending queue.
Talgorithm ¼ T 6 T 4 Time between starting and completing the function
block’s encapsulated functionality.
Tfinish ¼ T 8 T 6 Time from finishing the encapsulated functionality and
triggering the output event.
The relationship between these timing points are depicted in Figure 2.3; the
points where the input and output data from the function block change are also
shown. It should be noted that the standard assumes that events behave as discrete
points in time and have no duration. In a physical system, events may require the
transfer of some form of state change information between blocks and may have a
short but finite duration.
The IEC 61499 model assumes that there are no input event and data queues
associated to a function block’s inputs. However, the standard defines that the
execution environment needs to assure that only one input event is delivered at any
Tsetup
Tstart
Talgorithm
Tfinish
Input data
1 2 3 4 5 6 7 8
Input event
Output data
Output event
Figure 2.3 Execution timing

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CELESTIAL PHENOMENA.—MAY.
BY D. W. BELISLE.
COMA BERENICES.—This is a beautiful cluster of small stars,
situated about five degrees east of the equinoctial colure, and midway
between Cor-Caroli on the north-east, and Denebola on the south-west.
The stars that compose this group are small, but very bright, and are in
close proximity to each other; therefore the cluster is readily
distinguished from all others. There is a number of small nebulæ in this
assemblage, which give it a faintly luminous appearance, somewhat
resembling the milky-way. The whole number of stars in this cluster is
forty-three. It comes to the meridian on the 13th of May.
This constellation is of Egyptian origin. Berenice was married to
Evergetes, King of Egypt, and, on his going out to battle against the
Assyrians, she vowed to dedicate her hair, which was of extraordinary
beauty, to the goddess of beauty, if her lord returned in safety.
Evergetes returned victorious, and, agreeably to her oath, her locks
were shorn and deposited in the temple of Venus, whence they shortly
disappeared, and the king and queen were assured by Conon, the
astronomer, that they had been taken from the altar by Jupiter and
placed among the stars; and, to convince them of the truth of his
assertion, pointed out this cluster, and
There Berenice's locks first rose so bright,
The heavens bespangling with dishevelled light.
This group being among the unformed stars until that time, and not
known as a constellation, the king became satisfied with the declaration
of Conon, who, pointing to the group, said, There, behold the locks of
our queen. Berenice was not only reconciled to this petty larceny of

Jupiter, but was proud of the partiality of the god. Callimachus, who
flourished before the Christian era, thus adverts to it—
Immortal Conon, blest with skill divine,
Amid the sacred skies beheld me shine;
E'en me, the beauteous hair, that lately shed
Refulgent beams from Berenice's head;
The locks she fondly vowed, with lifted arms,
Imploring all the powers to save from harm
Her dearer lord, when from his bride he flew,
To wreak stern vengeance on the Assyrian crew.
CORVUS.—This small constellation is situated east of the Cup, and
may be readily distinguished by four bright stars of the third magnitude,
which form a trapezium; the two upper ones being three and a half
degrees apart, and the two lower ones six degrees apart. Algorab, the
most eastern star of these four, forms the east wing of the Crow, and
comes to the meridian on the 13th of May. Beta, in the foot of the
Crow, is seven degrees south of Algorab, and is the brighter of the two
lower stars; and on the left, six degrees west of Beta, is Epsilon, which
marks the neck, while two degrees below it is Al Chiba, a star of the
fourth magnitude, which marks the head.
This constellation is of Greek origin, and it is gravely asserted by
their ancient historians that this bird was originally of the purest white,
but was changed, for tale-bearing, to its present color.
The raven once in snowy plumes was drest,
White as the whitest dove's unsullied breast,
Fair as the guardian of the capitol,
Soft as the swan, a fair and lovely fowl;
His tongue, his prating tongue, had changed him quite
To sooty blackness from the purest white.

Apollo, becoming jealous of Coronis, sent a crow to watch her
movements. The bird discovered her partiality for Ischys, and
immediately acquainted the god with it, which so fired his indignation:
that
The color left his look,
The wreath his head, the harp his hand forsook;
His silvered bow and feathered shafts he took,
And lodged an arrow in the tender breast
That had so often to his own been prest.
To reward the crow, he placed it among the constellations. Other
Greek mythologists assert that it takes its name from a princess of
Phocis, who was transformed into a crow by Minerva to rescue the maid
from the pursuit of Neptune. One of the Latin poets reverts to it thus—
For, as my arms I lifted to the skies,
I saw black feathers from my fingers rise;
I strove to fling my garments on the ground,
My garments turned to plumes and girt me round;
My hands to beat my naked bosom try,
Nor naked bosom now nor hands had I;
Lightly I tripped, nor weary, as before,
Sunk in the sand, but skimmed along the shore,
Till, rising on my wings, I was preferred
To be the chaste Minerva's virgin bird.
VIRGO.—This constellation lies directly south of Coma Berenice, and
east of Leo. It occupies considerable space in the heavens, and
contains one hundred and ten stars. It comes to the meridian the 23d
of this month. Spica Virginis, which marks the left hand of the Virgin, is
a star of the first magnitude, and is of great brilliancy, and, with
Denebola in Leo, and Arcturus in Boötes, forms a large equilateral
triangle, which, joined with Cor-Caroli, a star of the same brilliancy, at
an equal distance north, forms the Diamond of Virgo. The stars in this

diamond are of equal brilliancy, rendering it one of the most clearly
defined and most beautiful figures in this part of the heavens.
This constellation is probably of Egyptian origin. A zodiac discovered
among the ruins of Estne, in Egypt, commences with Virgo, and,
according to the regular progression of the equinoxes, this zodiac must
be two thousand years older than that at Dendera. This relic of the
earliest ages of the human species is conjectured to have been
preserved during the deluge by Noah, to perpetuate the actual
appearance of the heavens immediately subsequent to the creation.
The Athenians also claim the origin of this constellation, maintaining
that Erigone was changed into Virgo. Erigone was the daughter of
Icarius, an Athenian, who was slain by some peasants whom he had
intoxicated with wine; and it caused such a feeling of despair in
Erigone, that she repaired to the wood and hung herself on the bough
of a tree.
Thus once in Marathon's impervious wood,
Erigone beside her father stood,
When, hastening to discharge her pious vow,
She loosed the knot and culled the strongest bough.
ASTERION ET CHARA.—This is a modern constellation, and
embraces two in one. It lies north of Coma Berenice, and west of
Bootes, and comes to the meridian the 20th of May. Cor-Caroli is the
brightest star in this group, and marks Chara, the southern hound.
Asterion is north of this, and is marked by a small star about three
degrees above Cor-Caroli. These two hounds are represented as
chasing the Great Bear around the Pole, being held in a leash by
Bootes, who is constantly urging them on in their endless track. The
remaining stars in this group are too small and scattered to excite
interest.

URSA MAJOR.—This constellation is situated between Ursa Minor on
the north, and Leo Minor on the south, and is one of the most
conspicuous in the northern hemisphere. It has been an object of
observation in all ages of the world. The shepherds of Chaldea, Magi of
Persia, priests of Belus, Phœnician navigators, Arabs of Asia, and
American aborigines seem to have been equally struck with its peculiar
outlines, and each gave to the group a name which signified, in their
respective languages, the same thing—Great Bear. It is somewhat
remarkable that nations which had no knowledge or communication
with each other should have given the same name to this constellation.
The name is perfectly arbitrary, there being no resemblance in it
whatever to a bear or any other animal.
This cluster is remarkable for seven of its brightest stars forming a
dipper, four stars forming the bowl, and three, curving slightly, shaping
the handle. These seven stars are of uncommon brilliancy, and need no
description to point out their locality. The whole number of stars in this
group is eighty-seven, and it comes to the meridian the 10th of May.

MANUFACTURE OF PINS.
WE often hear the expression used, when talking of anything
comparatively useless, that it's not worth a pin; and from this we
might be led to suppose, did we not know it to be otherwise, that a pin
was a very worthless thing, instead of being what it is—one of the most
useful that is manufactured in this or in any other country. As the use of
pins is principally confined to the female portion of our community,
perhaps the following short account of their manufacture, for which we
are indebted to Knight's Cyclopædia of Industry, a very useful book,
may not be uninteresting to our readers:—
Pins are made of brass wire. The first process which it undergoes,
by which any dirt or crust that may be attached to the surface is got rid
of, is by soaking it in a diluted solution of sulphuric acid and water, and
then beating it on stones. It is then straightened; after which, it is cut
into pieces, each about long enough for six pins. These latter pieces are
then pointed at each end in the following manner: The person so
employed sits in front of a small machine, which has two steel wheels
or mills turning rapidly, of which the rims are cut somewhat after the
manner of a file: one coarse for the rough formation of the points, and
the other fine for finishing them. Several of these pieces are taken in
the hand, and, by a dexterous movement of the thumb and forefinger,
are kept continually presenting a different face to the mill against which
they are pressed. The points are then finished off by being applied in
the same manner to the fine mill. After both ends of the pieces have
been pointed, one pin's length is cut off from each end, when they are
re-pointed, and so on until each length is converted into six pointed
pieces. The stems of the pins are then complete. The next step is to
form the head, which is effected by a piece of wire called the mould,
the same size as that used for the stems, being attached to a small axis
or lathe. At the end of the wire nearest the axis is a hole, in which is
placed the end of a smaller wire, which is to form the heading. While
the mould-wire is turned round by one hand, the head-wire is guided by

the other, until it is wound in a spiral coil along the entire length of the
former. It is then cut off close to the hole where it was commenced,
and the coil taken off the mould. When a quantity of these coils are
prepared, a workman takes a dozen or more of them at a time in his
left hand, while, with a pair of shears in his right, he cuts them up into
pieces of two coils each. The heads, when cut off, are annealed by
being made hot and then thrown into water. When annealed, they are
ready to be fixed on the stems. In order to do this, the operator is
provided with a small stake, upon which is fixed a steel die, containing
a hollow the exact shape of half the head. Above this die, and attached
to a lever, is the corresponding die for the other half of the head,
which, when at rest, remains suspended about two inches above the
lower one. The workman takes one of these stems between his fingers,
and, dipping the pointed end of a bowl containing a number of heads,
catches one upon it and slides it to the other end; he then places it in
the lower die, and, moving a treadle, brings down the upper one four or
five times upon the head, which fastens it upon the stem, and also
gives it the required figure. There is a small channel leading from the
outside to the centre of the dies, to allow room for the stem. The pins
are now finished as regards shape, and it only remains to tin or whiten
them. A quantity of them are boiled in a pickle, either a solution of
sulphuric acid or tartar, to remove any dirt or grease, and also to
produce a slight roughness upon their surfaces which facilitates the
adhesion of the tin. After being boiled for half an hour, they are
washed, and then placed in a copper vessel with a quantity of grain tin
and a solution of tartar; in about two hours and a half, they are taken
out, and, after being separated from the undissolved tin by sifting, are
again washed; they are then dried by being well shaken in a bag with a
quantity of bran, which is afterwards separated by shaking them up and
down in open wooden trays, when the bran flies off and leaves the pins
perfectly dry and clean. The pins are then papered for sale.
Pins are also made solely by machinery. There is a manufactory for
this sort (the Patent Solid Headed Pins, near Stroud) where nearly
3,250,000 are made daily.
A pin, then, is not such an insignificant article, after all. We see it
has to go through a great many processes and hands before it is

finished. If we take one, examine it closely, and mark how nicely it is
made, how neatly the head is fixed on to the shank, how beautifully it
is pointed, and how bright it shines, we shall see a very good specimen
of what the ingenuity and labor of man can do upon a piece of metal. It
is really surprising what a large number are made, and how many
persons are employed in their manufacture. We read, some time ago,
an amusing article from Bentley's Miscellany, wherein the writer asks
the question: What becomes of the pins? and puts forth the rather
curious assertion that, if they continue to be lost and made away with
as they are now, some day or other the whole globe will be found to be
one vast shapeless mass of pins.
In conclusion, we would recommend our readers always to bear in
mind the excellent maxim which Franklin attached to a pin, namely, A
pin a day, a groat a year.

ADVICE TO A BRIDE.
I BEG to remind my daughter that the husband has a thousand
elements of disturbance in his daily avocations to which his wife is an
utter stranger; and it will be her privilege, and her title to the respect of
all whose respect is worth having, to make his own fireside the most
attractive place in the universe for the calm repose of a weary body or
excited mind. The minor comforts, which are the most valuable,
because the most constantly in requisition, will depend more upon her
look, her manner, and the evidence of her forethought, than upon all
the other occurrences of life.—Parental Precepts.

TRUTH STRANGER THAN
FICTION.
MR. GODEY: Miss Snipe left my house in great haste on the second
day of April, forgetting, in her precipitation, several articles of her
wardrobe and her portfolio. While waiting an opportunity to forward
them to Wimpleton, a natural impulse of curiosity induced me to
examine the contents of the portfolio, when, lo and behold, a letter,
directed to yourself, fell on the floor. Being loosely folded and unsealed,
I ventured to open it, supposing it merely a business communication.
Imagine my surprise on discovering the nature of its contents, for I had
been unable to penetrate the reasons of her hurried departure; but do
not, I pray you, accuse me of having read it through.
Finding, as far as I proceeded, nothing very heinous laid to myself,
nor any insinuations against my table, I judge proper to forward it
without delay, according to the address. However, I can with difficulty
forgive her for calling my boy a cub, and think, moreover, that her
dislike towards my Irish inmate is unreasonable. As to Mr. Sparks—I do
not blame her so much—he has not yet paid me those gloves. And as
to the writer herself, I am really astonished—we all thought her such a
quiet and unobservant little body—on becoming acquainted with this
spirited volley from her pen. Will there not be both laughing and wry
faces in my household, if you publish it? And, though April is gone (I
am sorry the letter was not sooner found), do give the world the benefit
of her experience, to oblige and amuse
Yours, faithfully,
HELEN MASHUM.
April 1, 1854.

MY DEAR MR. EDITOR: Such a tumult as we have all day been in, by
reason of that abominable practice of fooling, has been enough to
destroy the patience of a saint. I am nearly out of my wits. Here have I
come, at my niece's invitation, to spend a fortnight with her, in a
boarding-house. She was lonely, she said; Mr. Sparks was so much at
the office; and it would be such a favor if I could stay with her a few
days.
So I have come from my quiet country home, fifteen miles off, to
this noisy town that calls itself a city, to visit Ann Sophia; and, between
you and me, I was an April fool from the beginning. There are several
other young married women boarding in the same house, who, like my
flighty niece, have apparently nothing under the sun to do but go
shopping and pop in and out of each other's rooms. Some of them are
in her parlor every evening when she is not out at parties or lectures,
and, as she spins street yarn every morning, I cannot for the life of me
see what opportunity she takes to be lonesome. But I do see that she
gives herself no time to keep her husband's shirts made up and in
order; and I find that I have no lack of employment, for she has kept
me sewing ever since I came.
Sophy, dear, says I, the morning after my arrival, give me some
sewing; I cannot be idle, and have nothing but this knitting to do for
myself.
Whereupon she brought out a whole piece of fine bleached cloth,
and proposed that we should amuse ourselves by making it into shirts
for her husband.
Holton needs them so much, said she, and you are so kind as to
offer your services, aunty; it would cost so much to hire them done,
and his salary is so small now, you know, and boarding so expensive.
And to work we began; but the truth is that it is very little which
Ann Sophia has done thus far. Well, what is a single woman good for
unless to make herself generally useful? A precious sight of twaddle
have I read first and last in the papers and magazines about the
delights and privileges of old-maidery. Delights of a fiddlestick! Pulled
hither and thither, perhaps—as I have been—at the beck of married
brothers and sisters, and a score of idle nephews and nieces; if you

have a home of your own, not allowed to stay at it in peace for more
than one week together. Sister Julia's children have all got the measles,
and Aunt Abigail must go and take care of them; or brother Peter's wife
is dead, and Abigail must pack up and go to keep house for him till she
becomes attached to the motherless tribe, and feels quite at home
among them, when he gets a new wife, and Abigail departs just as she
begins to be happy. To crown all, when she puts her own house in
order, and has a nice lot of sweetmeats and pickles made up, along
comes a troop of relations, male and female, young and old, to visit
dear Aunt Abigail and eat up all her stores, to say nothing of completely
kicking out the stair carpet. But I am wandering from my subject—a
thing which I am apt to do.
The house is quiet now, and, having finished one of Holton Sparks's
shirts this evening, I embrace the respite to retire to my own room.
After all, I do not feel like scolding about Ann Sophia. The pleasant-
tempered girl looks so much like her mother, brother Peter's first wife; I
brought her up, too, at least till she was ten years old, when her father
married again. Her chief fault is her youth, and she will get over that,
dear child.
However, to return, I cannot sleep till I have expressed my
indignation at the follies that have been perpetrated in honor—rather
should I say, in dishonor—of All Fools' Day, hoping that you, Mr. Editor,
will lift your voice in favor of putting a stop to such absurdities. In the
first place, I had scarcely risen, when I was myself made the victim of
imposition; for, while I was dressing, there was a rap at the door, and I
heard Sparks's voice—
Aunt Abigail, are you up? Here is a letter postmarked Wimpleton. It
came by the night train, probably.
As sure as fate, thought I, there has something dreadful
happened at home. And, being much agitated, I tore open the envelop
in great haste, without observing that the superscription was not in
brother Sam's hand, and wondering why Sparks did not wait to learn
the nature of its tidings. As truly as I am a living woman, there was
nothing inside but a great foolscap sheet, and on it these words, in
staring capitals—

APRIL FOOL.
I could have cried, so vexed was I at first. Then I felt thankful that
no bad news had actually reached me; for, during the brief moment
occupied in opening the letter, you can scarcely imagine the many
terrible things that passed through my head. Mother had had a fit,
fallen down and broken her leg, though brother Sam had promised me
faithfully not to leave her alone while I was gone; or that stupid Dutch
boy, who takes care of the cow and the fires, had left live coals in the
ash-box, and the house was burned to the ground. Or Sam himself had
got one of those severe attacks of inflammatory rheumatism, and
nobody there but mother to take care of him, and take his fretting into
the bargain, and she almost eighty years old. When I recovered myself
a little, I took that wretched sheet of paper, and was on the point of
penning a dignified expression of my sentiments below the odious
words, and handing it in silent scorn to my nephew-in-law at the
breakfast-table. But better feelings prevailed; I smoothed it nicely in my
portfolio, and am now scratching this hasty epistle upon its surface,
intending in the morning to write it more legibly on some of my own
fair sheets of Bath.
A few among the follies of this tiresome day have, I must
acknowledge, given me a certain sort of satisfaction. Holton Sparks has
been come up with himself; not by any means of mine, I earnestly
assure you, for, besides heartily despising it, I cannot in any shape
perpetrate April fooling. Sam often says that this is because I am so
matter-of-fact; but, matter-of-fact or not, I trust that there is not
enough matter-of-folly in my composition to attempt such
performances. I always did abominate practical jokes, and Sam knows
that; yet the jokes which that boy still puts upon me, though I am three
years older than himself, would be deemed improbable.
Well, when the breakfast-bell rang this morning, I went down stairs
with an air as erect and dignified as a woman of fif——no matter—with
such a demeanor as one who has outlived the fooleries of early youth
should make habitual. Holton Sparks is very fond of eggs, and
invariably takes the biggest on the dish. I observed that our landlady
directed the servant to hand them first to Mr. Sparks, who was too
intent on securing his egg to notice her action. Indeed, he never

hesitates to help himself first, quite regardless of the ladies who sit
near, and even of Ann Sophia. Holton is a tremendous eater, seeming to
think of nothing at table but disposing of his food as rapidly and in as
large quantities as possible. The manner of this gentleman is to place a
large piece of nicely buttered toast on his plate, pour the egg over it,
pepper the whole thoroughly, and swallow it as if the preparation were
some unpleasant dose that it is his duty to dispatch. Mrs. Mashum, who
is altogether too much given to laughing, and too volatile for her
station, sat behind the coffee urn shaking violently with suppressed
mirth. He broke the shell of his egg as usual, when, behold, his plate
was flooded with a dingy-looking liquid, which proved to be warm dish-
water. On comprehending the joke, he sent it away with an offended
air, and made his breakfast on beefsteak, without deigning to join in the
universal laugh. It seems that last evening he laid a wager with Mrs.
Mashum that she could not succeed in playing him a trick, he should be
so constantly upon his guard during All Fools' Day. The affair of the egg
has put him out of humor to such an extent that we have been saved
the infliction of any more jokes at his hands. He has worn his dignity all
day, not even Ann Sophia succeeding in laughing or coaxing him into
laying it aside. I rather think that he grudges the dollar which he will
have to lay out for the gloves, as Mrs. Mashum has won the bet, and
Ann Sophia assures him that a pair of her own will not do by any
means. He proposed that expedient to settle the matter. Holton is
stingy. But his wife declared that such a good joke deserved a pair of
Alexander's best. It is not because I approve of betting that I mention
this, for I hold the practice in great abhorrence. It was only of a piece
with the other follies of the day, and shows up Holton Sparks a little.
A small fire of fooling was kept up throughout the morning. If the
door-bell has been rung once, it has forty times, by Mrs. Mashum's cub
of a boy, who would jerk the handle or toss up his ball at the wire, and
then run out of sight. In going from my own room to my niece's, I saw
a sixpence on the floor, and, stooping down to pick it up, found it fast.
Congratulating myself on not having been observed, I was passing on,
when that disagreeable urchin shouted, from behind a door—
April fool, old lady!
He deserves to be sent to the House of Refuge.

Ann Sophia herself has put me out of all manner of patience by
saying, as I sat sewing at the front window in her parlor, Pray, Aunt
Abigail, whose carriage do you suppose that is? when no vehicle was
in view but the milkman's. Or, suddenly, she would exclaim, What
ladies are those crossing the street? when none were anywhere to be
seen.
But the meanest of all was a very rude thing, which she repeated
several times upon different persons, apparently delighted with its
efficacy. This was to rush up suddenly, and screaming out, See there!
throw her arm directly across one's nose with so much force as to
oblige that organ to follow the direction of her outstretched finger,
whether or no. Such a sort of fooling by compulsion struck me as
particularly reprehensible.
I'd try it on you, aunty, said the volatile child, if I were not afraid
of scoring my arm.
Such an insinuation against my nose! Had it been any one besides
Sophy, I could not have forgiven the speech. She is such a highty-
tighty.
But one trick which she played was really good, especially as its
object was a man to whom I have taken a huge dislike. He is an Irish
gentleman connected with some legal firm in town, most desperately
polite, with a very long round nose and fiery red hair. He is continually
poking dishes at me across the table, and is fairly oppressive with his
attentions. Moreover, he calls me Mrs. perpetually. Mrs., indeed!
Intimating that I am old enough to be a Mrs., if not one in fact. As he
rises very late, he never appears at breakfast with ourselves; but at
dinner we have the misery of his presence. To-day, when we were
almost through with the first course, he entered with an air much
flushed and uncomfortable.
Are you ill, Mr. O'Killigan? asked Mrs. Mashum.
No, thank you, madam, said he, with one of his customary efforts
at politeness. But I have been trying for a long while to shave, till
forced in despair to give up the attempt. The deuce has got into my
soap.

You have forgotten that it is the first of April. The day may have
had some influence upon your dressing-case, remarked one of the
ladies present.
I declare, I have not thought of that, said he, and, springing from
the table, he ran to his room, returning with something which he
begged the ladies to examine. It proved to be a thick, fair slice of a raw
potato, in size and color so much like his own soap, which had been
removed, that he had detected no difference, except that it refused to
form a lather. This was the work of my mischievous niece, who looked
at it very gravely, and remarked, with much demureness—
I always knew that you Irish were fond of potatoes, but was not
aware that you carried it to such an excess as to shave with that
vegetable.
It would have better pleased me had O'Killigan been angry; but the
Irishman took the joke, and all the speeches made at his expense, with
entire good-humor, laughingly assuring the ladies that he would be
revenged before night. And, as he knew not whom to suspect, he
adopted a course which involved most of us in its consequences. When
we retire for the night, those who are not better provided equip
themselves with a candle, of which a supply stands ready in the lower
hall. Such a fuss as I had with my light this evening! It went out as
soon as I reached my own door; and, after relighting it several times by
means of matches, the tallow was exhausted, and I discovered that the
blackened remnant of wick was stuck into a carrot. That miserable
Irishman had enlisted Biddy Flyn, the chambermaid, in his service, and
this afternoon they spent two whole hours in the basement at their
nefarious work, trimming off carrots and giving them a very thin coating
of grease. Mrs. Mashum herself did not escape, for, just as she began
taking her usual rounds to see that all was safe for the night, her
treacherous light went out, leaving her in total darkness—in the lower
regions, too, for she was on the point of inspecting a keg of mackerel in
the cellar.
At this identical moment, having used up all my matches in vain
endeavors to light a candle, which, like its manufacturer's locks, I had
found to be carroty, I was on my way to the kitchen in pursuit of a

more reliable means of illumination, when I heard Mrs. Mashum scream
out—
Bring a light, Biddy, for goodness sake! I shall step into this rat-trap
that you've set, if I stir an inch in the dark.
And all the while the shameful Biddy stood holding her sides, and
laughing in a most unreasonable way. Several persons were running
along the upper hall calling for lights, the ladies in a sort of demi-toilet,
and one of the young men, a dry-goods clerk, who dresses his hair with
a curling-tongs, having on a black silk night-cap. But the real culprit did
not suffer, after all, for Ann Sophia has her own solar lamp.
While these distressing events were transpiring, that mean
Irishman, with his big nose and red head, sat in the parlor, as cool as
possible, reading the London News by the light of a brilliant
camphene lamp. I wonder his hair did not ignite and cause an
explosion. It would have served him quite right.
Strange to say, Mrs. Mashum is not at all offended either at
O'Killigan or his accomplice, but has enjoyed their mischief in a way to
me utterly unaccountable. I suppose Sam would say that she knows
how to take a joke; for my part, they are things which I do not wish to
know how to take myself; I wash my hands of all participation in such
knowledge.
I have obtained a lamp that shall last till I have finished this
narrative of to-day's outrageous proceedings. On passing the parlor-
door, I heard that disagreeable O'Killigan say to his landlady, in reply to
some of her pretended threats of punishment—
At any rate, my good Mrs. Mashum, you cannot arrest me for
incendiary attempts; I have made such laudable exertions to put out
the flames in the house.
Impudent fellow! I had a mind to say something about the blaze on
his own head; but I forbore, passing on in offended silence.
Now, my dear Mr. Godey, set a good example, and lead the way in a
reform of these abuses, as you have in so many other praiseworthy
undertakings. Frown upon these April fooleries, especially as levelled at
the peace and quiet of respectable single women. If my letter is too

late to take effect this present season, please give it due notice before
a twelvemonth hence. You will thus oblige and gratify your friend and
constant reader,
ABIGAIL SNIPE.
Postscript. I shall go home to-morrow, and finish Holton Sparks's
last new shirt in the pleasant seclusion afforded by my own
hearthstone. I cannot endure the thought of sitting at the table in this
house any longer, opposite that dreadful O'Killigan, hearing him crack
his dry jokes while he rubs his chin with his thumb and forefinger. To be
obliged to listen when he comments on the mishaps of this evening
would surely set me into a nervous fit. It strikes me that I have read in
one of Sam's old books—Sal somebody's writings—of an elderly lady
who died of a Frenchman. If I were to stay here much longer, I
should assuredly die of this middle-aged Irishman.
Depend upon it, I shall not breathe a word to Sam of my trials at
Sophy's boarding-house, in consequence of the inmates all making fools
of themselves and me on the FIRST OF APRIL.

INTELLECTUAL ENDOWMENTS OF
CHILDREN.
AN extremely intelligent boy, of about twelve years of age, was once
brought to the late Dr. Deville, an English phrenologist, for examination,
by a parent who was very proud of the intellectual endowments of his
child. Dr. Deville gave his opinion of the boy's character, at the same
time cautioning the father of the dangerous course he was pursuing.
But the father's reply was, All that other boys considered labor and
hard study were merely child's play to him; and that his studies could
not be hurtful to him—he enjoyed them so much. Again Dr. Deville
endeavored to save the child, but the father would not attend to the
warning. Two years from that time he again called on Dr. Deville, and,
in reply to his inquiries about the child, burst into tears, and stated that
the boy was an idiot.

GODEY'S COURSE OF LESSONS IN
DRAWING.
LESSON V.
The outline of the stem and the curve of the scroll of Fig. 54 must
first be drawn, the distances and proportions of the various parts being
carefully observed. In sketching the scroll in Fig. 55, the eye alone will
be the guide, the directions and distances of the various parts being
marked off before filling in the details.

The method of drawing the rosette forming part of the scroll shown
in Fig. 57 is displayed in Fig. 56, the circle being drawn first.
In sketching Fig. 58, the direction of the curve must first be
ascertained, its due proportions noted, thereafter filling in the details.

The stem, leaves, flower, and buds of the wall-flower in Fig. 59 will
afford an interesting example for practice at this stage of progress; the
stem, its length and direction, should first be drawn, the position of the
leaves, c. marked thereon, and the details thereafter filled in.

The sketch in Fig. 60, which represents the stem, leaves, and flower
of the yellow crowfoot, will be drawn in the same way as above.
The flower of the honeysuckle in Fig. 61 affords a good example for
free pencil-sketching. The stem should be drawn first, then an outline
made which will touch all the exterior parts of the sketch, as in Figs. 44
and 52; the distances of the leaves should next be drawn on this, and
the details put in. The pupil should endeavor to copy this example
correctly; it may appear very difficult, but, by a careful attention to the
rules we have given, and a little determination to try again, if
perchance she should once or twice fail, the difficulty will soon vanish.
Fig. 62.
The sketch in Fig. 62, representing a human foot, may be put in by
first drawing the general outline, thereafter finishing the details. Figs.
63, 64, and 65 will be drawn in the same manner.

DRESS—AS A FINE ART.
BY MRS. MERRIFIELD.
CONCLUSION.
WE look forward hopefully to a day when art-education will be
extended to all ranks; when a knowledge of the beautiful will be added
to that of the useful; when good taste, based upon real knowledge and
common sense, will dictate our fashions in dress as in other things. We
have schools of art to reform our taste in pottery, hardware, and textile
fabrics, not to speak of the higher walks of art, painting, sculpture, and
architecture. The handle of a jug, the stem of a wine-glass, the design
for dress silks or lace veils, will form the subjects of lectures to the
students of the various schools of design; disquisitions are written on
the important question whether the ornamental designs should
represent the real form of objects, or only give a conventional
representation of them, while the study of the human figure, the
masterpiece of creation, is totally neglected, except by painters and
sculptors. We hope that the study of form will be more extended, that it
will be universal, that it will, in fact, enter into the general scheme of
education, and that we shall hereafter see as much pains bestowed in
improving by appropriate costume the figure which nature has given us,
as we do now in distorting it by tight stays, narrow and high-heeled
shoes, and all the other deformities and eccentricities of that many-
faced monster, fashion. The economy of the frame, and the means of
preserving it in health and beauty, should form an integral part of
education. There can be no true beauty without health, and how can
we hope to secure health if we are ignorant of the means of promoting
it, or if we violate its precepts by adopting absurd and pernicious
fashions?

Surely it is not too much to hope that dress-makers will hereafter
attend the schools of design, to study the human form, and thence
learn to appreciate its beauties, and to clothe it with appropriate dress,
calculated to display its beauties to the greatest advantage, and to
conceal its defects—the latter with the reservation we have already
noticed. We hope, also, that the shoe-maker will learn to model the
shoe upon the true form of the foot.
Manufacturers are now convinced of the importance and utility of
schools of design, and whether the article hereafter to be produced be
a cup and saucer, a fender, a pattern for a dress or for furniture, for a
service of plate or diamond tiara, it is thought proper that the pupil, as
a preliminary course that cannot be dispensed with, should commence
with the study of the human figure. Yet, is not dress an art-
manufacture as well as a cup and saucer, or a tea-board? Are there less
skill and talent, less taste required to clothe the form which we are told
is made after God's own image, than to furnish an apartment? Why
should not dressmakers and tailors attend the schools of design as well
as those artisans who are intended to be employed in what are now
called art-manufactures? Why should not shoe-makers be taught the
shape and movements of the foot? If this were the case, we are
satisfied that an immediate and permanent improvement would be the
consequence in our style of dress.
We believe that many portrait painters stipulate that they shall be
allowed to dictate the dress, at least as regards the arrangement of the
colors, of their sitters; the reason of this is that the painter's selection
of dress and color is based upon the study of the figure and complexion
of the individual, or the knowledge of the effects of contrast and
harmony of lines, tissues, and colors, while the models which are
presented for his imitation too frequently offer to his view a style of
dress, both as regards form and color, which sets the rules of harmony
at defiance. Now, only suppose that the dress-maker had the painter's
knowledge of form and harmony of lines and colors, what a revolution
would take place in dress? We should no longer see the tall and the
short, the slender and the stout, the brown and the fair, the old and the
young, dressed alike, but the dress would be adapted to the individual;
and we believe that, were the plan of study we recommend generally

adopted, this purpose might always be effected without the sacrifice of
what is now the grand desideratum in dress—novelty.
The reasons why the art of dressmaking has not hitherto received
the attention which it deserves, are to be sought for in the constitution
of society. The branches of manufacture which require a knowledge of
design, such as calico-printing, silk and ribbon-weaving, porcelain and
pottery, and hardware manufactures, are conducted on a large scale by
men of wealth and talent, who, if they would compete successfully with
rival manufactures, find it necessary to study and apply to their own
business all the improvements in science with which their intercourse
with society gives them an opportunity of becoming acquainted. It is
quite otherwise with dressmaking. A woman is at the head of every
establishment of this kind a woman generally of limited education and
attainments, from whom cannot be expected either liberality of
sentiment or enlarged views, but who possibly possesses some tact and
discrimination of character, which enable her to exercise a kind of
dictatorial power in matters of dress over her customers; these
customers are scarcely better informed on the subject than herself.
The early life of the dressmaker is spent in a daily routine of labor
with the needle, and, when she becomes a mistress in her turn, she
exacts from her assistants the same amount of daily labor that was
formerly expected from herself. Work, work, work with the needle from
almost childhood, in the same close room from morning to night, and
not unfrequently from night to morning also, is the everlasting routine
of the monotonous life of the dressmakers. They are working for bread,
and have no leisure to attend to the improvement of the mind, and the
want of this mental cultivation is apparent in the articles they produce
by their labor. When one of the young women who attend these
establishments to learn the trade thinks she has had sufficient
experience, she leaves the large establishment and sets up in business
on her own account. In this new situation, she works equally hard, and
has therefore no time for improving her mind and taste. Of the want of
this, however, she is not sensible, because she can purchase for a trifle
all the newest patterns, and the thought never enters her poor little
head that the same fashion may not suit all her customers. This
defective education of the dressmakers, or rather their want of

knowledge of the human form, is one of the great causes of the
prevalence of the old fashion of tight-lacing. It is so much easier to
make a closely-fitting body suit over a tight stay than it is on the pliant
and yielding natural form, in which, if one part be drawn a little too
tight, or the contrary, the body of the dress is thrown out of shape.
Supposing, on the other hand, the fit to be exact, it is so difficult to
keep such a tight-fitting body in its place on the figure without securing
its form by whalebones, that it is in vain to expect the stays to become
obsolete until the tight-fitting bodice is also given up.
This will never take place until not only the ladies who are to be
clothed, but the dressmakers shall make the human form their study,
and direct their efforts to set off their natural advantages by attending
to the points which are their characteristic beauties. A long and delicate
throat, falling shoulders, not too wide from point to point, a flat back,
round chest, wide hips; these are the points which should be developed
by the dress. Whence it follows that every article of dress which
shortens the throat, adds height or width to the shoulders, roundness
to the back, or flatness to the chest, must be radically wrong in
principle, and unpleasant and repulsive in effect. In the same manner,
whatever kind of dress adds to the height of a figure already too tall
and thin, or detracts from the apparent height of the short and stout,
must be avoided. These things should form the study of the
dressmaker.
As society is now constituted, however, the dressmaker has not, as
we have already observed, leisure to devote to studies of the necessity
and importance of which she is still ignorant. The reform must be
begun by the ladies themselves. They must acquire a knowledge of
form, and of the principles of beauty and harmony, and so exercise a
controlling influence over the dressmakers. By this means a better taste
will be created, and the dressmakers will at length discover their
deficiency in certain guiding principles, and will be driven at last to
resort to similar studies. But in this case a startling difficulty presents
itself—the poor dressmaker is at present over-worked: how can she find
leisure to attend the schools of design, or even pursue, if she had the
ability, the necessary studies at home? A girl is apprenticed to the trade
at the age of thirteen or fourteen, she works at it all her life, rising

early, and late taking rest, and what is the remuneration of her daily toil
of twelve hours? Eighteenpence, or at most two shillings a day, with her
board! As she reckons the value of the latter at a shilling, it follows that
the earnings of a dressmaker, in the best period of her life, who goes
out to work, could not exceed 15s., or at the most 18s. a week, if she
did not, at the hazard of her health—which, indeed, is frequently
sacrificed—work at home before she begins, and after she has finished
her day's work abroad. The carpenter or house-painter does not work
harder, or bring to bear on his employment greater knowledge than the
poor dressmaker, yet he has 4s. 6d. a day without his board, while she
has only what is equivalent to 2s. 6d. or 3s.! What reason can be
assigned why a woman's work, if equally well done, should not be as
well paid as that of a man? A satisfactory reason has yet to be given;
the fact, however, is indisputable that women are not in general so well
paid for their labor as men.

LETTERS LEFT AT THE PASTRY-
COOK'S:
BEING THE CLANDESTINE CORRESPONDENCE BETWEEN KITTY
CLOVER AT SCHOOL, AND HER DEAR, DEAR FRIEND IN TOWN.
EDITED BY HORACE MAYHEW.
THE FIFTH LETTER LEFT.
(Written on copy-book paper, apparently left by hand.)
SHOWING WHAT KITTY THOUGHT OF GOVERNESSES IN GENERAL,
AND OF ONE IN PARTICULAR.
NELLY, dearest, I have formed a great determination. Nothing shall
ever induce me to become that poor, absurd, ill-used creature, called a
governess. I would starve sooner, or make shirts (which is pretty nearly
the same thing), or emigrate and marry the first savage I met, or be a
touter at a bonnet shop, or even go into service at a cheap lodging-
house; anything, Nelly, sooner than be turned into that hopeless,
spiritless, friendless being a governess seems destined by nature, or
society, to be.
A governess in a private family is bad enough, but then she is not
totally deprived of the comforts of home. She has a room, or at least a
bed, entirely to herself, and her meals are generally the same as those
of the family. Besides, a certain degree of respect is always paid to her.
The servants are obliged to treat her with civility, at all events in the
presence of their mistresses; and the mistresses are compelled to show

her a little attention, if it is only done to set a good example to their
servants. Then, again, their young charges cannot invariably be
amusing themselves at her expense. They cannot always be teasing
her. When they are taken out for an airing in the carriage, or when they
are brought down after dinner with their shiny faces and glossy ringlets,
or whenever there is company, or their parents and strangers are
present, the governess enjoys a brief respite from that system of petty
tyrannies she is the untiring victim of elsewhere. She has her few
pleasures, though perhaps they may come at long straggling intervals;
she has her distractions, her excitements in moving about in the world,
and going to places of public amusements, and occasionally she knows
what it is to enjoy the sweet success of rivalry—for have we not seen,
Nelly, many a poor neglected governess who was doing the work of a
musician at the piano, without his wages, receive in the course of the
evening more attention than the fine young ladies themselves who
were the worshipped idols of the establishment?
But the governess in a girls' school has a very different life of it,
Nelly. She hasn't a moment to herself. She is the first to rise and the
last to go to bed. She hasn't even the privacy of a bedroom to herself,
for she is obliged to sleep in the same room as the girls, to look after
them. The only privacy she knows is when she creeps into bed and
draws the curtains round her. Our play-hours are no play-hours to her;
rather on the contrary, for then her torments really begin, and only end
when the bell rings again for class. She is the target at which every
little chit fires her fun, and thinks she has a perfect right to do so. She
is the only game at which the girls never tire of playing, and to see how
they enjoy it you would imagine there was no amusement like it. It is
true, Nelly, I have not seen much misery yet, and hope I never shall;
but I can hardly imagine anything in this world more miserable than a
school governess on a half-holiday.
Why, look at poor Blight. I have only to look upon her to feel for the
sufferings of the whole class. Her nature seems to be sun-dried. She
never smiles, and there is such an air of resignation about her, such a
tone of despair that runs through all her words and smallest
movements, that it is perfectly clear Hope never whispers into her ear

any of those soft motherly words which soothe the agony of one's heart
and lull it quietly off to sleep.
She may justly be called our mistress of all work. She does a little
of everything; she helps the smallest girls to dress; takes the junior
pupils; hears the reading; sees to the wardrobes; gives out the linen;
teaches needlework; and superintends the Saturday night's cleaning; in
short, she is expected, as they say of servants, to make herself
generally useful, which means, in our instance, that she is worked to
death by everybody, and spared by nobody; besides being teased,
deceived, bullied, and ridiculed by every one who has a fancy that way;
and for leading a life like this, she only gets 16l. a year, and her board
and lodging during the holidays!
Snapp (another of our teachers) smiles at Blight's old-fashioned
learning. She says it is quite out of date, and only fit for a charity
school. Mademoiselle (the French teacher) quizzes her dress, and
makes fun of her melancholy, and talks of her contemptuously, as, ça,
which I am told is the same as if you were speaking of a cook, or a
poor relation, and called her it. Fraulein (the German mistress) mimics
her, and laughs over her patient endurance and old-maidish manners.
It must be confessed that poor Blight's appearance affords plenty of
temptation for this cruel ridicule. She is certainly very ugly, and no one
ever loses an opportunity of telling her so. The worst is, the example
set by the schoolmistress is followed with the greatest zest by the
schoolgirls, who indulge in all kinds of practical jokes at her expense.
She is unfortunately very short-sighted, and consequently they are
always hiding her spectacles, or else rubbing the glasses over with
butter or ink. No one considers there is any harm in this, for the girls
have grown to look upon Blight as fair game; and if any one can put
her into a passion, it is considered rare fun, and thought just as
harmless as throwing bread-pills at one another when the mistress's
back is turned. When there is no other amusement going on, the cry is
always raised, Let's go and tease Blight, and you see the whole school
rushing forward as eagerly as if a gypsy suddenly appeared at the play-
ground gate to tell us our fortunes. But if any one is in trouble, Blight is
the first to screen her. If any girl is ill, Blight will sit up with her all
night, and will pet and nurse the little sufferer until she almost fancies

herself at home; and when the little invalid has grown well again, and
has recovered the use of her tongue and fingers, Blight never says a
word about the ungrateful return, but bears it all like a martyr, which, in
truth, she really is. Ugly as she is, I really think there are times when I
could throw my arms round her neck, and kiss her for her goodness.
I cannot tell you all the nicknames which they have for her face and
person, nor would it altogether be agreeable for you, Nelly, I think to
hear them. Suffice it to say, the poor thing, is very old—thirty-nine, if
she is a day; and she has the funniest little head of hair, every hair
appearing to be pulled as tight, and to be almost as wide apart, as the
strings of a harp. The top of her head is mounted with a round knot of
hair no bigger than the worsted ball you see on a Scotch cap. It's a
wonder to me she doesn't wear a wig or a cap of some sort, though
perhaps it would be too dangerous, as every one would undoubtedly be
trying to pull it off. The girls declare no one can recollect her having a
new gown. Every quarter a very thin, snuff-brown silk, on a very stiff
lining, is brought out as Sunday best; but it is only the old one turned
and altered a bit, for that little wicked thing, Jessie Joy, put a drop of
ink on one of the breadths on purpose to find it out; and there it is still,
journeying about backwards and forwards, first in front and then
behind; now on the top, just under her chin, and next down at the
bottom, sweeping the floor, precisely as the faded silk is twisted or
turned to hide the creases and the ravages of old age. The girls
calculate the period they have been at school by this venerable gown;
and it's no unusual thing to hear them, when disputing about any
particular date, settling it at once by referring to the age of Miss Blight's
brown silk, saying, I recollect very well it was in the ninth quarter of
Blight's Sunday gown; and a reference to a date of this kind is
considered as indisputable as to a Family Bible, or an old almanac.
But these are small matters, Nelly, which I am half ashamed to tell
you, for under this poor garment there is a heart of so much goodness
as to make us wonder at the strange hiding-places in which virtue
sometimes delights in lurking, as if from modesty it had taken every
precaution not to be found out. What do you think, Nelly? I am told by
Meggy that poor Blight supports an old bedridden mother! She has no
positive proof of this, but she is morally sure of it. This, then, accounts

for the reason why the poor governess is always working so hard—
never resting from crocheting purses, and knitting antimacassars
sufficient to cover all the sofas in the world. If you ask her for whom
she makes this extraordinary quantity (you can't think, Nell, how quickly
and beautifully she works), she simply replies, her pale face becoming
paler, for a dear friend; and that is all we can get out of her to reward
our vulgar curiosity. This must be the truth, for at all hours, both early
and late, has she got a needle in her hand. There is a story that she
wakes up sometimes in the middle of the night, and works whilst the
girls around her are sleeping. But no one knows the cause of her
excessive industry, and I really think she would be miserable if it were
known, and her fingers would not ply their work of love half so nimbly if
she suspected that the girls, as they watched her with such fixed
curiosity, were acquainted with the sacred object for which she was
toiling. It is a puzzle when or where she sells all the things she finishes,
and no one exactly likes to find out, though one or two attempts have
been made, but always ending, I am happy to say, in the most
complete failure. It makes me sad to watch her anxiety when there is a
postman's knock at the door. She starts up in her seat, and pauses for a
while in her work (the only pause it ever knows), until she gives out the
letters; and then you would pity her with all your heart to see how
disappointed she is—what a vacancy of hope falls like a dark shadow
upon her face—when she learns that there is not one for her! Though,
when there is a letter, it is scarcely any better. She sighs heavily, looks
sometimes at a little locket she carries in her breast, and hurries on
with her work quicker than ever, as if the purse she was finishing was
to contain her own money instead of somebody else's, and she had so
much that she wanted the use of it immediately.
If you have any fancy-work you want doing (any braces or cigar-
cases you wish to give away as presents), will you send it to me, Nelly,
and I will ask Blight, if I can do so without offending her, to do it for
me?
I'm obliged to finish my letter, Nelly, for the fact is I have been
writing the latter part of it in our bedroom with a piece of wax candle I
took out of a candlestick there was in the hall, and there is only just

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