Lectura 2.3 soa-overview-directions-benatallah

Service Oriented Architecture:
Overview and Directions
Boualem Benatallah and Hamid R. Motahari Nezhad
School of Computer Science and Engineering
The University of New South Wales
Australia
{boualem,hamidm}@cse.unsw.edu.au

1

Introduction

The push toward business automation, motivated by opportunities in terms of
cost savings and higher quality, more reliable executions, has generated the need
for integrating the different applications. Integration has been one of the main
drivers in the software market during the late nineties and into the new millennium. It has led to a large body of research and development in areas such as
data integration [26], software components integration, enterprise information
integration (EII), enterprise applications integration (EAI), and recently service
integration and composition [2,11,16,12].
Service oriented architectures (SOAs) provide an architectural paradigm and
abstractions that allow to simplify integration [2,21]. There a number of technologies available to realize SOA. Among them, Web services and the set of related specifications (referred to as WS-* family), and also services that are built
following the REST (REspresentation State Transfer) architecture [8] (called
RESTful services) are gaining the momentum for integration at the data level.
One of the main facilitators of integration in WS-* approach is standardization. Standardization is a key to simplifying interoperability: instead of having
to interact with heterogeneous systems, each with its own transport protocol,
data format, interaction protocol, and the like, applications can interact with
systems that are much more homogeneous. More specifically, Web services standards foster support of loosely coupled and decentralized interactions mainly at
the application level. The main feature of RESTful approach is the simplicity
of service development and usage. This architectural style has been adopted in
the offering of data services [4,1] which is a major advance in data-level integration. AJAX [9], which is an enabler of an ad-hoc service composition approaches
known as mashups [17], is also based on REST. Mashup applications enable integration at the presentation level. This refers to integration of graphical user
interfaces (GUIs) of applications.
In this chapter, we briefly survey the different specifications and approaches
in SOA and evaluate them in terms of their contributions to integration. We
propose a conceptual framework for understanding the integration problem as
well for analyzing existing solutions. We believe that viewing the different approaches to interoperability in the context of this framework will make it easier
E. B¨rger and A. Cisternino (Eds.): Software Engineering, LNCS 5316, pp. 116–130, 2008.
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c Springer-Verlag Berlin Heidelberg 2008

Service Oriented Architecture: Overview and Directions

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to identify the commonalities and contrasts of existing standards and speciﬁcations, discover gaps, and better leverage existing standards to provide automated
support to Web service interoperability.
In the following, in Section 2, we present the conceptual framework in terms
of integration layers going from low level, which are horizontal, to higher levels,
which may not be needed in all integration scenarios (Section 2.2). Next, we
provide an overview of integration solutions before SOA in the context of proposed architecture (Section 2.3). In Section 3, we introduce the main existing
technologies for realization of SOA (Section 3.1). Then, we use the proposed
integration layers to evaluate SOA realization approaches (Section 3.2). In Section 4, we outline future directions in SOA to further help developers and users
in simplifying the problem of integration, and conclude this chapter.

2
2.1

Software Integration
Motivating Example

As an example, consider the two business enterprises depicted in Figure 1, exposing their functionalities as services. Integration is important in two diﬀerent
scenarios: integrating internal systems of each enterprise (referred to as “enterprise application integration” (EAI), as well), and integration with external
entities (referred to as “business-to-business integration” (B2B), as well). In the
internal of an enterprise, there is a need to integrate data and applications related to various systems. For instance, if these enterprises work in the domain
of procurement and sales in a supermarket chain, then they may maintain a
database for storing procurement data and a database for storing inventory and
sales data. They may also need a data warehouse (DW) for storing historical
sales transactions, which needs to collect and integrate data from these two data
sources. Each of these enterprises may also implement a business process for

Fig. 1. Integration scenarios: EAI (enterprise application integration) and B2B
(Business-to-Business)

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B. Benatallah and H.R. Motahari Nezhad

fulfilling its business objectives, which describes how, e.g., orders are processed
from the time that they arrive up to the time that goods are shipped, in terms
of data and control flows.
From the perspective of external interactions, the pre-requisite is that services
on each enterprise can communicate seamlessly (e.g., exchange messages) with
those of its partner. In addition, there may be a need for properties such as security and guaranteed delivery. Furthermore, advanced features such transactions
may be needed in the interactions between the two enterprises. Moreover, they
should be able to understand the content of exchanged messages. The developers of the client enterprise also need to understand the order in which messages
are expected by the partner services, which is captured in the business protocol
of the services. Similarly, policies that govern the interactions between services
should be known to service clients. Finally, developers in each enterprise may
need to integrate results retuned from partner services, e.g., the current location
of a shipment, with other external services, e.g., Google map, to visualize it at
the presentation level.
In the following, we use the above description of requirements to present
different layers of integration.
2.2

Integration Layers

By analogy with computer networks, we believe it is useful to study the integration in terms of layers, which address various parts of problem at different level
of abstractions (Figure 2). Typically, the structuring in layers goes from lower
level layers, which are more horizontal (needed by most or all interactions), to
higher layers, which build on top on the lower ones and may or may not be
needed depending on the application.
Communication layer. The first step for any application to interact to each
other is to be able to exchange information. This is mainly achieved through the
definition and using a protocol for transporting information, regardless of the
syntax and semantics of the information content. Examples of such protocols
are HTTP for transforming information on the Internet, IIOP in CORBA, and
VAN in EDI standards [16].
Data layer. The integration at this layer means that the applications should
seamlessly understand the content of data (documents and messages) that are
exchanged between them. The interoperability issues at this layer occur in the
syntax, structure and semantics of the data elements in the exchanged information. Integration at this layer is mainly achieved through offering mediators and
languages (e.g., ETL) for transformation and mapping to convert data from one
format to another. Although much progress has been made to facilitate datalevel interoperation, however, still there is no silver bullet solution [26]. Given
the current advances, users still play a major role in identifying the mismatches
and developing their mappings and transformation.


Application

Application

Presentation Layer

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Presentation Layer
Policies and nonfunctional properties

Business Protocol

Business Protocol

Functional Interface

Functional Interface

Basic Coordination

Basic Coordination

Data Layer

Data Layer

Communication Layer

Business Logic Layer

Policies and nonfunctional properties

Communication Layer

Fig. 2. Application integration layers

Business logic layer. Integration at this layer refers to integrating standalone
applications with defined interfaces (APIs), behavioral constraints, and also nonfunctional constraints. Integration at this layer can be divided into the following
sub-layers:
– Basic coordination. This layer is concerned with requirements and properties related to the exchange of a set of message among two or more partners.
For example in both EAI and B2B scenarios, two services may need to coordinate to provide atomicity based on 2-Phase commit. Other examples of
specifications at this layer are federated security management specifications.
We consider this kind of coordination to be horizontal, meaning that such
coordination are generally useful and can be applied in many business scenarios, and that is why we consider it at a lower level of abstraction in the
business logic layer.
– Functional interfaces. The interface of a service declares the set of operations
(messages) that are supported by the application. For example, a procurement service provides operations to lodge an order, and track its progress.
As another example, a data service provides operations to access and manipulate data. The integration at this layer may imply finding correspondences
and the mappings between the signatures of operations of the two services
to be integrated.
– Business protocol. The business protocol gives the definition of the allowed
operation invocation (or message exchange) sequences. Heterogeneities between business protocols can arise due to different message ordering constraints, or due to messages that one service expects (sends) but that the
interacting partner is not prepared to send (receive). For example, a service
may expect an acknowledgment in response to a sent message, while the
partner does not issue such message.
– Policies and non-functional properties. The definition of an application may
include policies (e.g., privacy policies) and other non-functional properties

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(e.g., QoS descriptions such as response time) that are useful for partners to
understand if they can/want interact with the application. The interoperability issues at this layer can be categorized into two classes: in expressing
policies, in which case they are similar to those of data layer. For example,
two applications may declare conceptually equivalent policy assertions, but
using different syntax (i.e., element names), structure (i.e., element type and
values) and semantics. The other class of interoperation issues refers to differences between the policies of two applications. For instance, differences
in the offered/expected quality of service, e.g., response time, price, etc.
Resolution of mismatches of this type may require negotiation and making
agreements between applications.
Presentation layer. The integration in this layer refers to constructing applications by integrating components at the graphical user interface (UI) level [5].
UI-level integration fosters integration at a higher level of abstraction, where
graphical representations of components are composed to build a new application. Integration issues at this layer include definition of a language and model
for representation of components so that the integration is facilitated [5].
2.3

Integration Technologies before SOA

In this section, we give a brief overview of main integration technologies prior
to Web services, and other realization of SOA.
2.3.1 Data Integration
Data integration has been subject of research for many years most notably in the
context of databases [13,26]. The goal of data integration systems is to build applications by integrating heterogeneous data sources. Data integration systems
have three elements: source schema, mediated (target) schema, and the mapping
between them. Source schema refer to the data model of data sources to be
integrated, mediated schema is the view of the integrated system from the existing data sources, and the mapping provide mechanisms for transforming queries
and data from the integrated systems to those of data sources. A closely related
area in this context is the schema mapping that aims at providing automated
assistance for mapping schema definition of one data source into another [23].
These provide techniques for identifying syntactic, structural and semantic heterogeneities between schemas.
Note that in data integration systems, little cooperation from the component
applications is needed, as one can always tap into the applications databases,
e.g., by the means of SQL queries. The drawback of this approach is that it
requires a significant effort to understand the data models and to maintain the
mediated schema in the wake of changes in the data sources. In data integration
systems, the integration is achieved through building new applications through
composition of data sources at the data layer, and integration at the communication layer is achieved through tight coupling with integrated data sources.


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2.3.2 Business Logic Integration
The integration of applications at the business logic level has been thoroughly
studied in the last thirty years giving rise to technologies such as remote procedure calls (PRCs), object brokers (such as DCOM and CORBA), message
brokers, electronic data interchange (EDI) and also standard specifications such
as RosettaNet [2]. We can broadly categorize exiting solutions into RPC-based
and message-oriented approaches.
Examples of RPC-based approaches include DCOM, Java RMI and CORBA,
which enable calling operations on remote interfaces and so to integrate applications. They provide mechanisms for communication level integration, as well,
but leave the data-level integration to approaches in data integration systems.
On the other hand, message-oriented approaches such as EDI and RosettaNet
target integration at the business process (business protocol) level through standardization. EDI provides VPN network and associated protocols for integration
at the communication layer, and proposes to address data level issues through
offering standardized business document formats. RosettaNet mainly provides
specifications for integration at the business protocol level between applications.
Finally, message-oriented middleware, suited for EAI scenarios, fosters integration through establishing a shared communication medium between parties, and
the development of adapters (see [2,16,12] for a comparative study of these
approaches).

3

Service Oriented Architecture

Service Oriented Architecture (SOA) is an architectural style that provides
guidelines on how services are described, discovered and used [2,21]. The purpose
of this architecture is to address the requirements of application development for
distributed information systems, which are loosely-coupled and potentially heterogeneous. In SOA, software applications are packaged as “services”. Services
are defined to be standards-based, platform- and protocol-independent to address interactions in heterogeneous environments. In the following, we give on
overview of main realization of SOA and compare them in the context of proposed integration layers.
3.1

SOA Realization Technologies

Currently, there are four main approaches in SOA that provide specifications and
standards for interoperation among services: the WS-* family, ebXML1 , semantic
Web services 2 , and REpresentational State Ttansfer (REST)-ful services.
The WS in WS-* family stands for “Web Services”. Web services have become the preferred implementation technology for realizing the SOA paradigm.
Web services rely, conceptually, on SOA, and, technologically, on open standard specifications and protocols. WS-* specifications are a group of standards
1
2

http://www.ebXML.org
http://www.daml.org/services

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mainly proposed by industrial software vendors that develop specifications in an
incremental and modular manner: specifications are introduced in a bottom-up
fashion where the basic building blocks are simple, horizontal specifications. The
specifications stack is gradually extended, with specifications at a higher level of
abstractions built on top of more foundational ones.
ebXML (Electronic Business XML) is a joint initiative of the United Nations
(UN/CEFACT) and OASIS3 as a global electronic business standard. ebXML
provides a framework for business-to-business integration and introduces a suite
of specifications that enable businesses to locate their partners and conduct business based on a collaborative business process. It takes a top-down approach by
allowing collaborations between partners to come up with a mutually negotiated
agreement at a higher level, i.e., business process and contracts, and then working down towards how to exchange concrete messages. The technical architecture
of ebXML provides a set of specifications for following fundamental components:
(i) business process specification schema (BPSS) provides a framework to support execution of business collaborations consisting of business transactions, (ii)
messaging services and security (ebMS), (iii) collaboration protocol profile and
agreements (CPP/A), and (v) core components.
The semantic web services (SWS) aims to provide Web services with a rich
semantic description of capabilities and contents in unambiguous and computerinterpretable languages to improve the quality and robustness of activities in
the lifecycle of Web services including service discovery and invocation, automated composition, negotiation and contracting, enactment, monitoring and recovery [15,14,3]. Current efforts in this area can be organized into two categories,
both of which assume using of a shared ontology between trading partners: (i)
bringing semantic to Web services by defining and using semantic Web markup
languages such as OWL-S [15], or WSMO [3], and (ii) incorporating semantic
information by annotating messages and operations (supported by ontologies)
of Web service specifications such as WSDL using their extensibility points and
offering specifications such as WSDL-S [14].
The key component of the first category is using a language for the description of Web services. OWL-S (formerly known as DAML-S) is an OWL-based
ontology for Web services in this category. OWL-S consists of three interrelated
subontologies, known as the serviceProfile, serviceModel, and serviceGrounding.
The serviceProfile expresses what a service does in terms of functional and nonfunctional properties, and its role is similar to CPP in ebXML-based approach.
The serviceModel describes how a service works in terms of the workflow and
possible execution paths of the service. The serviceGrounding maps the abstract
constructs of the process model onto concrete specifications of message format
and protocols. WSMO is another proposal in this area, which focuses more on
providing a framework for developing semantic Web services. For comparison of
OWL-S and WSMO refer to [22]. Here, we only discuss WSDL-S and OWL-S
approach, which is currently more mature, compared to WSMO.

3

http://www.oasis-open.org


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REST is an architectural style that identifies how resources in a network, and
specially World Wide Web, are defined, addressed and can be accessed [8]. In
this architecture, applications in the network are modeled as a set of resources,
which are uniquely addressable using a URI. Each resource also supports a constrained set of well-defined operations, and a constraint set of content types,
e.g., XML, HTML, CSV, text, etc. REST adopts HTTP protocol for communication between resources, and therefore, the core operations of REST, i.e., GET,
POST, PUT, and DELETE are those of HTTP. REST promotes a client-server,
stateless and layered architecture. Due to its simplicity, which makes it scalable
to the Internet, it has been adopted for implementing services (such services
are called RESTful services). A client application that interacts with a resource
(service) should know its URI address and can request to execute one of the core
REST operations on the resource. The client should also know the data format
of the output data. Therefore, the client developer has to read the documentation of the service to make it work with the service, or the data format may be
shipped along with the message content.
The main differences between RESTful services with WS-*, which using SOAP
on top of HTTP to provide additional functionalities, include: (i) RESTful services rely on a small set of domain-independent operations (e.g., GET to retrieve a representation of resources and PUT to update resources), while in
SOAP-based services operations are defined in a domain-specific manner (e.g., a
procurement service may offer a createPurchaseOrder operation), and (ii) REST
works based on currently used Web standards such as HTTP and SSL. However,
SOAP-based approach proposes a suite of extensible specifications to enable advanced functionalities such as reliable messaging, message-level and federated
security and coordination, etc. RESTful services have been widely adopted for
offering a significant number of simple services over the Internet, and they have
gained remarkable popularity among developers. For instance, in Amazon Web
services, the usage of their RESTful services far exceeds using its SOAP-based
Web services although developers have to read textual description of RESFTful
services to understand how to develop clients to interact with them.
It should be noted that another key distinction between above approaches is
that WS-* and ebXML approaches are industry initiatives, while SWS is mainly
promoted by academia. REST architectural style is proposed in the academic
environment, but it has been favored by industry.
3.2

Analysis of SOA Approaches Using Integration Layers

Figure 3 compares the above four approaches of SOA realizations in various
integration layers. As it can be seen WS-* family of approaches, semantic Web
services, and ebXML target integration at the business logic level. On the other
hand, RESTful services mainly intend to simplify integration at the data layer,
and recently they have been also used for integration at the presentation layer [5].
There has been an extensive study on comparison of standardization efforts
in WS-* family, semantic Web services and ebXML (the reader is referred to
[12,24,18]). In the following, we only focus on emerging technologies in this area,


Presentation

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WS-SecurityPolicy

OWL-S Profile

ebXML CPP

OWL-S
Service Model

WS-Policy

ebXML
BPSS, CPA

OWL-S Profile,
OWL-S Grounding

ebXML CPP

B. P.

WSCDL
BPEL WSCI
S
C WS-Conversation
A
HTTP

WSDL

Communication

Data

Coord.

Intf.

Business Logic

Policies

Mashups (AJAX)

WSDL-S

WS-Coordination
ebXML BPSS

BTP, WS-Transaction
XML, HTML,
text, JSON, etc

SDO
XML

OWL

WS-Security, WS-Reliability, WS-Addressing,
SOAP Attachments

XML
ebMS

SOAP
HTTP (SSL)
RESTful

HTTP, SMTP. FTP
WS-*

Semantic WS

ebXML

Fig. 3. The comparison of SOA realization approaches in the context of proposed
integration layers

and in particular, data services, which are RESTful services and target the data
integration layer, service component architecture (SCA) for integration in the
business logic layer, and finally mashups for the integration at the presentation
layer.
3.2.1 Data Level Integration: Data Services and SDO
Over the last few years, there has been an enormous increase in the number of
distributed data sources, which are needed to be accessed over networks, and
more notably over the Internet. The concept of “service” in SOA has provided a
proper abstraction for wrapping and offering application over the Internet. This
abstraction has been adopted to expose data sources with different types over
the Internet. The term data services, coined by Microsoft4 , is used to refer to
such services [4,1]. Data services provide solutions for integration at the data
layer. Data services can be used to provide virtual, aggregated views of data in
multiple data sources. Hence, a data service provides data mediation, integration
and also an abstraction for the underlying data sources. They simplify the data
access, integration and manipulation. Data services also can be used to expose
data integration systems as services.
4

Astoria project, http://astoria.mslivelabs.com


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To implement data services, REST architecture is adopted, due to its simplicity, so that they can be accessed over HTTP and identified using a URI. The
data in a data service is represented using an abstract model, called entity data
model, which is an extended form of entity-relationship model. A data service
can be configured to return the data in several formats including XML, JSON5 ,
RDF+XML, text, etc. It supports HTTP GET method for accessing data and
HTTP methods such as PUT, POST or DELETE to manipulate data through
the data service.
Integration at the data layer is also needed in business logic layer integration
approaches. In such scenarios, data has to be exchanged between services and
non-services applications (e.g., Java programs) and other data sources. XML
has been adopted as the data format by WS-* family, which is intended for
integration at the business logic layer (see Figure 3). To facilitate data exchange
between both services and non-services and data sources using a single format a
generic data format called service data objects(SDO)6 is introduced. SDO offers
more than a data format. Indeed, it provides a data programming architecture
and a set of APIs for accessing and manipulation of data.
SDO architecture consists of three components: data objects, data graph, and
data access service. Data objects contain a set of named properties that contain
data elements or refer to another data objects. There are also data object APIs
to access and manipulate the data. Data graphs are in fact envelops for data
objects, which are transported between partner applications. Data graphs keep
the track of changes in data objects by partner applications. Data graphs can
be constructed from data sources, e.g., XML files, relational databases, EJBs,
and services, e.g., Web services, and adapters (implementing data mediation and
transformations). Finally, data access services are the software components that
populate data graphs from data sources and services, and manipulate the data
graph based on manipulation of data sources.
“Data access services” in SDO play a similar role to that of “data services”
above. However, SDO provide a more rich data representation, exchange and manipulation approach made for data integration over heterogeneous data sources
in an enterprise. SDO approach targets data integration with business logic level
integration solutions. SDO offers a programming platform for data integration,
and hence should be used by integration developers. However, data services target data integration for end users or non-expert users. SDO is currently widely
supported in the implementation tools, and its specification has been sent to
OASIS for standardization.
3.2.2 Business Logic Level Integration: SCA
Web services (WS-*) approach mainly targets integration at the business logic
level (see Figure 3). The standardization in Web services simplifies interoperation at the business logic level from basic coordination layer to policies and nonfunctional properties. However, besides standardization, realizing SOA
5
6

http://www.json.org
http://www.osoa.org/display/Main/Service+Data+Objects+Home

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requires programming models, methodologies and tools to enable interoperation
and application integration. In addition, in an enterprise not only Web services,
but also existing functionalities that are not Web services have to be integrated
in building integrated applications. As the concept of service promotes reuse,
an important aspect is to provide a framework to support users in composing
services and other non-services functionalities, which can be exposed as services.
To fulfill the above requirements, a group of software vendors including BEA,
IBM, Oracle and SAP led an initiative represented by a set of specifications,
called service component architecture (SCA) 7 . The intention of SCA is to simplify the creation and integration of business applications using SOA paradigm.
In this architecture, an application is seen as a set of components (services),
which implement (service) interfaces. It provides abstractions and methodologies for component construction, component composition (assembly) and deployment. The framework is intended to be neutral to component implementations
(it supports as component implementation languages such as Java, BPEL, PHP,
C++, .NET, etc). The principle that this architecture follows is to separate the
business logic implementation from the data exchange between components.
SCA offers a service assembly models that is a framework for the composition
of components into bigger ones, which can be deployed to the server together,
or into systems that can be deployed separately. An SCA component (simple or
composite) can be exposed as a service, and can consume other external service
components. The communication between components is modeled using wires.
SDO data representation format (see Section 3.2.1) is developed to be used for
transportation of data on wires between components in SCA. Currently, SCA
has been submitted for standardization to OASIS.
Comparing SCA with other standard specifications (e.g., in WS-* family of
standards), it is not intended to address integration from one specific aspect.
However, it provides an architecture, programming models and abstractions to
support development of large scale systems using SOA across different layers in
the business logic level (see Figure 3). It builds on and exploits the offerings of
SOA and in particular Web services, and take the idea of “software as service”
one step ahead by enabling to expose business logic functionalities (developed in
different programming languages) as services that can communicate, be reused
and composed with other services.
3.2.3 Presentation Level Integration: Mashups
The integration problem at the communication, data, and business logic level
has been extensively studied, as discussed in previous sections. However, little
work has been done to facilitate integration at the presentation level. Since
development of user interfaces (UI) is one of the most time-consuming parts of
application development, testing and maintenance, the reuse of UI components is
as important as reuse of business logic [5]. Recently, the concept of Web mashups
and related technologies have been introduced, which take the first step in this
direction.
7

http://www.osoa.org/display/Main/Service+Component+Architecture+Home


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Web mashups are Websites or Web applications that combines content and
presentations from more than one source into an integrated experience [17].
Mashups are developed by compositing data, business logic (APIs) and UI of
existing applications or services. The difference with traditional integration approaches is that Web mashups also integrate UI components. Nowadays, mashups
are implemented using AJAX (Asysnchronous Javascript + XML) [9], but it is
not necessary to be implemented using it. AJAX follows the REST architecture
and aim to allow client side browser based applications to provide a rich and
responsive interface at the same level of desktop applications. It enables to send
requests to Web servers and services and receive responses without blocking.
The common principle in mashups is to quickly compose an application from
existing (REST, Javascript, RSS/Atom, and SOAP) services. Mashup applications usually combine services for unexpected usages. The main feature of
mashup, from an integration point of view, is that they allow for integration
at the user interface (presentation) level. Mashup can be also considered as an
ad-hoc approach for composition of existing content and services for building
situational applications (typically short-lived, and just-in-time solutions), which
is to the interest of many end users. To support development of mashup applications, numerous tools and frameworks have emerged recently to assist developers
and end users. Examples of these tools and frameworks are Yahoo Pipes8 , Google
Mashup Editor9 , Microsoft Popfly10 , and Intel Mash Maker11 .
Recently, a broader term, i.e., Web 2.0 [20] has been introduced to refer to all
user-centric creation, access and sharing of information and presentation components on the Web. Web 2.0 has transformed the way that end users are using the
Web. In Web 2.0, users collaborate and share information in new ways such as
social networking and wikis. Web 2.0 consists of a set of principles and practices
that makes the existing Web technologies more people centric. The common
principles of Web 2.0 include: (i) looking at the web as a platform that allows
extending the concept of service to any piece of data, software or application that
is exposed on the Web, (ii) using the collective intelligence (collaboration) to create, share, compose and refine applications. This mandates offering lightweight
programming models, and rich user interface. AJAX and mashups aim to provide
such programming language models and user interfaces.
The composition and integration in the mashups are mainly based on data flow
(e.g., a series operations performed on the data flowing from one component to
another in Yahoo Pipes), and synchronization is based on events (e.g., in using
Javascripts and receiving response) rather than ordered invocation of services,
which is the main approach in business logic level integration (e.g., WS-* family). It
should be noted that the mashups are about simplicity, usability and ease of access,
and that unlike WS-* approach or data integration approaches (e.g., ETL)this simplicity has the upper hand over completeness of features or full extensibility.
8
9
10
11

http://pipes.yahoo.com
http://editor.googlemashups.com
http://www.popfly.ms
http://mashmaker.intel.com

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4


Conclusions and Future Directions

As reviewed in this chapter, available approaches for realization of SOA remarkably simplify integration at the communication, data, and business logic
levels. This is achieved by proposing frameworks, abstractions and standardization efforts that increase the opportunities for homogeneities and unification of
communication protocols and data format for data exchange. However, the integration at the end user (presentation) level has not yet received the required
attention.
We believe the end users are the focus of next wave of research and development work in the various approaches in SOA both in RESTful services and
mashups, and also in WS-* family of specifications. As also can be seen in Figure 3, the presentation level integration for the RESTful services does not still
provide a full-fledged approach for integration, and there is no counterpart efforts
in WS-* approaches. One possible future direction could be also to adopt the
“service” concept as an abstraction for integration at the presentation level, so
that presentation components (and GUIs) are offered with published interfaces
that can be easily integrated and composed. Examples of initiative in this directions is Google Map APIs 12 . However, further end user level support is needed
as currently, such practices involves lots of low level scripting and coding, which
may not be convenient for end users.
The end-user driven trend in integration has also been witnessed by introduction of new concepts such as process of me by Gartner [10], and Internet
service bus [7]. Gartner report states that we should redefine processes in an
enterprise, and put the focus on people so that individuals have understanding and control of processes that they are involved in them. The process of
me includes integration of end user tools such as instant messaging, spreadsheets, threaded discussions and management of real-time events with business
process applications, and other Internet technologies based on Web 2.0. Therefore, a major enabler step for approaches that offer business logic integration
approaches (e.g., WS-* family) to fill this gap, and to support individuals (employees) by integration of ad-hoc personal and collaboration tools with processes
supported by traditional business applications. Realizing the concept of process
of me requires framework and tool support to allow users to define their own
views of the process execution in the enterprise with preferred end users-oriented
tools.
With a similar spirit, Internet service bus proposal takes the end user involvement to the next level by promoting the ideas of creating end user Web
applications on the Web and using the Web as an execution platform for end
user applications and other software and services. This idea can be seen as taking what SCA (and in general enterprise service bus) provides for professional
integration developers in composition of services and application and offering
them for end users. In such an environment end users should be supported in
the process of finding existing services and integrating them.
12

code.google.com/apis/maps


129

It should be noted that while SOA, and the abstraction of “service” simplifies
significantly the integration at various level, there is still the need for bridges,
mediators, adapters and mismatch resolution frameworks (e.g., data mediators,
business protocol adapters, and policies resolution frameworks). In fact, SOA,
and in particular standardization in SOA, reduces the opportunities of heterogeneities. However, at the higher levels of abstractions (e.g., business-level interfaces, business protocols, and policies), WS-* family offers languages to define
the service interface, business protocol and policies. There have been considerable research and development efforts in identifying and classifying mismatches
between such service specifications, and their resolution (e.g., see [19,6,25]). However, these approaches still involve many manual steps by the developers. Specially, there is a need for automated approaches for (simple) data mediation
between various formats at the end user side, when building mashup applications, and in spreadsheet environments, which are most popular tools for data
integration and manipulation.

Acknowledgement
Authors would like to thank the anonymous reviewers for their valuable feedbacks on the earlier draft of the chapter.

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