Web Services Computing Beyond Component-Based Architectures by vev19514


									           Web Services Computing: Beyond Component-Based Architectures

           Dr. Dionisis X. Adamopoulos                                Dr. Constantine A. Papandreou
 Dept. of Technology Education & Digital Systems                Hellenic Telecom. Organisation (OTE) and
           University of Piraeus, Greece                              University of Piraeus, Greece

                        Abstract                               (users, subscribers) a predefined, carefully selected, set of
                                                               capabilities / facilities regarding the integrated coverage
    Web services are emerging technologies that can be         of a (possibly) wide range of information and communi-
considered as the result of the continuous improvement of      cation needs, utilising the resources of (existing and fu-
Internet services due to the tremendous increase in            ture) telecommunication networks [1].
demand that is being placed on them. They are rapidly             This paper attempts to determine the boundaries of
evolving and are expected to change the paradigms of           Web service engineering and, considering the needs of
both software development and use, by promoting                companies that deploy Web services to support
software reusability over the Internet, by facilitating the    increasingly sophisticated business processes, proposes a
wrapping of underlying computing models with XML, and          framework for the development of Web services and
by providing diverse and sophisticated functionality fast      examines its main constituent parts, addressing important
and flexibly in the form of composite service offerings. In    issues for the creation and provision of a new generation
this paper, the different facets of Web services are           of functionally rich, adaptable, web-centric, composite
identified and a flexible approach to engineering complex      applications. Furthermore, it introduces the concept of
Web services is adopted in the form of a proposed              service grids as the necessary infrastructure that will
framework for the development of Web services. After the       enable Web services to transform the Web from a
examination of its main constituent parts, it is argued that   collection of information into a distributed computational
its full potential and that of Web service engineering in      entity, and identifies open matters and current technical
general, is realized through the gradual formation of a        challenges for the Web services community in association
rich service grid offering value-added supporting              with the proposed framework.
functionality and therefore the main desirable properties
of such a service grid are highlighted. Finally, the paper     2. Web service engineering
outlines a validation approach for the proposed
framework and assembles important pointers for future              A Web service is programmable application logic ac-
work and concluding remarks.                                   cessible using standard Internet protocols, fulfilling a spe-
                                                               cific task or a set of tasks and representing a discrete unit
                                                               of business or system functionality, that can be combined
1. Introduction                                                with other Web services to maintain business transactions
                                                               or workflows [3][7]. By exploiting Web services an
   Web-enabled service-oriented computing is becoming          organization is able to provide ("expose") any business
the prominent paradigm for distributed computing and e-        function to any other entity, such as another business
commerce, creating significant opportunities for a variety     function, an organization, a particular community, as well
of providers to develop value-added services by specify-       as end users. A Web service can be provided by the
ing new Web services or by combining already existing          organization directly, through trading networks or specific
ones. These services are self-contained, Web influenced        publishing hubs and other intermediaries on the Web.
programming entities capable not only of performing                Web services are self-contained, self-describing,
business activities on their own, but also possessing the      modular software entities that can be published, located
ability to engage other Web services in order to complete      and invoked across the Web. Each discrete Web service
higher-order business transactions. Therefore, Web ser-        can be deployed on and accessed from any node on the
vices can be considered as a special category of telematic     Internet, because once a Web service is deployed, other
services (new telecommunications services), that although      applications (and other Web services) can discover and
they have several unique characteristics, they remain geo-     invoke the deployed service. Therefore, multiple Web
graphically distributed entities (actually an encapsulation    services can be combined or assembled to form new
of a number of cooperating entities distributed over a         service configurations and deliver more valuable and
geographical environment) providing a number of people         sophisticated functionality supporting diversified business
objectives. In this way, Web services offer a degree of        maximise their usefulness, fulfil the emerging increased
flexibility and granularity not previously possible or         expectations regarding their value and impact, and lead
economically viable, as they facilitate on-the-fly software    eventually to a Web populated by a variety of service
creation through the quick assembly of loosely coupled,        objects. The most important requirements that Web ser-
reusable software components [4]. Furthermore, they can        vice engineering activities should support during their
interact with each other ("be orchestrated") in an infinite    desired evolution process are the following [1][3][4][5]:
variety of manners and through multiple iterations in          • The efficient and effective development of Web
order to deliver a particular task within any context [2].       services by guiding successfully service developers
    As a new domain or scientific discipline at the bounda-      during the entire Web service creation process.
ries of software engineering and telecommunications,           • The successful application in a Web services context
Web service engineering addresses the technologies and           (through the appropriate adaptation when necessary) of
engineering processes required to define, design, imple-         carefully selected concepts, models, techniques, design
ment, test, verify, validate, deploy, combine, maintain,         patterns and practices that are developed, tested and
and manage Web services that meet user needs in the              (extensively) applied during the creation of conven-
current or future networks. Its main objective is to ensure      tional telecommunications services.
the introduction of new and enhanced Web services and          • The reduction of complexity and the increase of
their management, in a fast and efficient manner. It relies      efficiency during the design and implementation of
heavily on open distributed object-oriented processing           Web services by hiding from the service developers
and Internet technology, and ambitiously promises to             commonly encountered implementation details.
significantly facilitate the offering of a wide variety of     • The efficient automation of the Web service creation
highly sophisticated and personalised services over the          process, without semantic loss, with the use of appro-
widest possible coverage area.                                   priate, carefully designed and tested, customisable, and
    Finally, it has to be stressed that Web services repre-      user-friendly software tools.
sent the convergence between Service-Oriented Archi-           • The development of a rich variety of Web services with
tectures (SOAs) and the Web. SOAs (as the one proposed           enhanced content, which can efficiently support a wide
by the Telecommunications Information Networking Ar-             range of communication, information, business, educa-
chitecture-Consortium, TINA-C) have evolved over the             tion, entertainment and cooperation needs.
last 10 years to support high performance, scalability,        • The representation, processing, management, and trans-
reliability and availability [1]. To achieve these proper-       mission (possibly in an integrated manner) of all the
ties, applications are designed as services, that can be         basic information types.
accessed through a programmable interface and run on a         • The adoption of precise service semantics, because in
cluster of centralized application servers. In the past,
                                                                 an open telecommunications market, it is important for
clients accessed these services using a tightly coupled,         reasons of service interoperability and for maximising
distributed object protocol, such as Microsoft’s DCOM,
                                                                 customer satisfaction to specify Web services in a clear
OMG’s CORBA or Sun’s Java RMI. While these proto-
                                                                 and unambiguous way by using concepts that their
cols are very effective for building a specific application,
                                                                 semantic content can be accurately defined.
they limit the flexibility of the system. Furthermore, each
                                                               • Reusability at different abstraction levels (e.g. reusable
of the protocols is constrained by dependencies on vendor
                                                                 service requirements, service specifications, service
implementations, platforms, languages or data encoding
                                                                 components), with the intention to promote rapid Web
schemes that severely limit interoperability and none of
                                                                 service design and deployment.
them operates effectively over the Web [2]. Web services
                                                               • The use of a variety of document types and their
inherit all the best features of the SOAs and all the best
                                                                 population with appropriate values so that they are
aspects of component-based development in general and
                                                                 semantically coherent and are interpreted correctly by
combine them with the Web. Like components, Web ser-
                                                                 the service requesters and providers.
vices represent functionality that can be easily reused
without knowing how the service is implemented. How-           • The management of Web services in a flexible manner.
ever, the Web supports universal communication using           • The interoperability of Web services in a multi-provider
loosely coupled connections and Web protocols are com-           (open) telecommunications environment (with multiple
pletely vendor-, platform-, and language- independent.           domains of management and ownership of services) by
                                                                 facilitating and promoting Web service composition.
3. A framework for the development                             • Openness to all types of potential end-users of a Web
                                                                 service considering all the possibly interested people
   of web services.                                              (e.g. mobile users, residential users, etc.).
                                                               • Openness to change of Web service software and hard-
   Because of the inherent complexity of Web technolo-
                                                                 ware (computer and network infrastructure), because as
gies and the recent diversification of the telecommunica-
                                                                 technology advances, or as prices change, or as pur-
tions environment, Web service engineering activities
                                                                 chasing policies and needs dictate, different hardware
should satisfy a number of requirements, in order to
  should be able to be used without requiring new in-                                                       • A Web service support environment: It is an
  vestment in the accompanying software, and vice versa.                                                      environment aiming to facilitate, both the development
• The accommodation of legacy telecommunications ser-                                                         of Web services (in cooperation with the Web service
  vices and systems as they represent significant invest-                                                     development methodology) and their execution under
  ments that should be protected.                                                                             real conditions. It consists mainly of:
• Security in each message exchange between a service                                                           − Web service engineering principles: These are
  requester and a service provider, which should be pri-                                                            concepts, guidelines, design patterns, practices and
  vate and unmodified, as well as non-reputable.                                                                    (in general) mental constructs that are applicable to
• The accommodation of relevant standards (if neces-                                                                Web service engineering activities.
  sary).                                                                                                        − A Web service architecture: It contains in a struc-
   Current Web service technology scores rather low                                                                 tured manner all necessary details for the informa-
compared to the above mentioned requirements. There-                                                                tion and computational modelling of Web services.
fore, in an attempt to revitalize Web service engineering
and enable it for the crucial role that is anticipated to have                                                  − A Web service execution environment: It encom-
in the new emerging telecommunications environment,                                                                 passes the necessary computing and network infra-
the Web service engineering framework of Figure 1 is                                                                structure and the appropriate ancillary software
proposed with the objective to provide a rich conceptual                                                            (e.g. operating systems, database management
model for the development and the description of Web                                                                systems, etc.), which is needed for and during the
services bringing this technology to its full potential.                                                            execution of a Web service. Its most important part
                                                                                                                    is the Web platform, which abstracts over all the
                                                                                                                    other parts and reduces greatly the effort needed
ASPs                                                                                            network
                                                                                                                    for the implementation of a Web service. Further-
                                                                                                                    more, the Web platform is accompanied by a

              The proposed framework
                                                                                                                    collection of software tools (together with a reuse
                   Web Service
                                                 Web Service
                                                                                 Web Service
                                                                                                                    infrastructure) that are used according to the Web
                                                                                 Environment                        service development methodology with the aim to
                   Transport (SOAP)                                                   Web
                                                                                                                    assist the service developer(s) when applying the
                   Description (WSDL)
                    Discovery (UDDI)
                                                              Service             engineering

                                                                                                               A Web services environment conforms to the
                       Web Services Platforms (.NET, J2EE)
                            C T
                             ore echnologies (XM SO , W L, U D
                                                L, AP SD D I)                                               conceptual roles and operations that characterize every
ISPs                           W   e b S e rv ic e E x e c u tio n E n v iro n m e n t
                                                                                                BSPs        SOA. The three basic roles are the service provider, the
        Business                                                                                            service consumer and the service broker (see Figure 2). A
                                                                                                            service provider offers the service and publishes the
Figure 1. The proposed Web service engineering                                                              contract that describes its interface. It then registers the
framework                                                                                                   service with a service broker. A service consumer queries
    As can be seen from Figure 1 the proposed framework                                                     the service broker according to its specific needs and
is placed inside a composite organisational context (a                                                      finds a compatible service. Then, the service broker
“business ecology”), in order to signify that Web service                                                   informs the service consumer on where to find the service
engineering activities are normally performed by a variety                                                  and its service contract. Finally, the service consumer
of entities / business formations. Although in practice                                                     uses the contract to bind the client to the service. In order
many of the companies operating in this sector / area                                                       for the three conceptual roles to accomplish the related
blend various functions into a composite offering and                                                       conceptual operations, a SOA system must supply /
adopt many different roles, the major players in this new                                                   specify three core functional architecture components;
always-on Web services landscape are Application                                                            namely transport, description, and discovery [7].
Service Providers (ASPs), Managed Hosting Providers
(MHPs), Internet Service Providers (ISPs), network                                                           Table 1. A comparison of SOA middleware and
operators, Independent Software Vendors (ISVs) and                                                                          Web Services
Business Service Providers (BSPs) [6]. Therefore, the                                                                       DCOM      CORBA      Java RMI        Web Services
                                                                                                            Invocation                CORBA                       JAX-RPC,
proposed framework is influenced by their business                                                          Mechanism
                                                                                                                            DCE RPC
                                                                                                                                                 Java RMI
                                                                                                                                                                  .NET, etc.
objectives, their general telecommunications and IT                                                         Data Format      NDR       CDR     Serialised Java      XML
strategic orientation, their knowledge, their problem                                                       Wire Protocol    PDU       GIOP        Stream           SOAP
                                                                                                            Transfer                                                HTTP,
solving attitude and their experience.                                                                      Protocol
                                                                                                                            RPC CO     IIOP        JRMP
                                                                                                                                                                  SMTP, etc.
    The main constituent parts of the proposed Web                                                          Interface        MIDL /   CORBA
                                                                                                                                               Java Interface       WSDL
service engineering framework, which are depicted in                                                        Description     DCE IDL    IDL
                                                                                                            Discovery                  COS
Figure 1, are:                                                                                              Mechanism
                                                                                                                                               Java Registry        UDDI
• A Web service development methodology: It is a
   methodology that guides service developers during the                                                       As can be seen in Table 1, the distributed object
   entire process of Web service creation.                                                                  platforms (middleware) that form the basis of SOAs
(DCOM, CORBA or Java RMI) define their own vertical                                               Service

set of formats and protocols to implement the core SOA                                            Broker

functions. This approach ensures consistency among
applications that share the same middleware, but prevents                 UDDI Inquiry
                                                                                                                        UDDI Publish

interoperability with applications that use different
middleware. It also requires that every service producer                                 Find               Register

and service consumer that engages in a conversation must                                                                            Description
have the appropriate middleware installed and loaded on
its computing infrastructure.                                               Service

    On the other hand Web services (Internet middleware),                                Client   SOAP

unlike traditional SOA systems, do not require an entirely     Figure 2. Conceptual roles and operations in a
new set of protocols. The most basic Web services proto-       Web Services Architecture (WSA)
col is XML (an industry standard), which is used as the           Furthermore, all Web services are currently composed
message data format and is also used as the foundation of      in a rather ad hoc and opportunistic manner by simply
all other Web services protocols. Web services use XML         combining their operations and input and output
to describe their interfaces and to encode their messages.     messages. If the requirements change or need to be
However, XML by itself does not ensure effortless com-         adjusted, then the composition will have to be respecified
munication. The applications need standard formats and         and recreated by possible interlinking additional or
protocols that allow them to properly interpret the XML.       modified service interfaces. This approach leads to a
Hence, the following XML-based technologies have               proliferation of badly specified service operations and
emerged as the de facto standards for Web services:            results in unmanageable and cluttered solutions. In this
• Simple Object Access Protocol (SOAP) establishes a           case, the needs of service developers that want to reuse
   common format for addressing messages and defines a         the design and implementation of existing Web services
   standard communications protocol for Web services.          only by extension or restriction, without developing them
• Web Services Description Language (WSDL) defines a           from scratch, cannot be satisfied.
   standard mechanism to describe a Web service.                  An equally important problematic situation arises also
• Universal Description, Discovery and Integration             from the fact that unlike a traditional telecommunications
   (UDDI) provide a standard and uniform mechanism to          enterprise network, many different providers share the
   register and discover Web services.                         multi-layered network and software infrastructure of Web
    These core Web service technologies define the trans-      services. While a particular group of dominant network
port, description and discovery mechanisms respectively        operators (telcos) provide backbone and last-mile wireline
in the way depicted in Table 1, and have a close relation-     network services, other providers contribute server
ship with a strong semantic underpinning. As most Web          management, data storage, edge cacheing, security, VPN
service configurations suggest, the three core functional      and wireless services, and several other ancillary services.
architecture components (transport, description, and dis-      Therefore, creating an integrated, end-to-end application
covery) are implemented using SOAP, WSDL, and                  delivery infrastructure incorporated into a Web service
UDDI, respectively, forming the Web Services Architec-         requires close cooperation between all the interconnected,
ture (WSA) that can be seen in Figure 2. A UDDI registry       autonomous participants (providers and enterprises).
has the role of a service broker. The register and find op-       It is evident that as Web services become more so-
erations are implemented using the UDDI Inquiry and            phisticated and more global in reach and capacity, it be-
UDDI Publish APIs. A WSDL document describes the               comes increasingly important to provide additional assis-
service contract and is used to bind the client to the ser-    tance to service developers in order to ensure the effective
vice. All transport functions are performed using SOAP.        encounter of the above mentioned problems and the effi-
    The Web Services Architecture (WSA) provides the           cient support of commercial-grade application functional-
necessary means to create Web services for the coverage        ity by Web services in an incremental manner, with little
of an infinite variety of needs and to dynamically             risk and at low cost. Recognising these needs, the Web
combine them to satisfy more specialized business re-          service development methodology of Figure 3 is pro-
quirements at any point in time, by knitting together          posed. This methodology “covers” in a systematic and
micro-services (individual process components) into a          structured manner the entire Web service creation process
broader application entity offering enriched functionality.    through a requirements capture and analysis phase, a Web
However, such Web service creation activities can be           service analysis phase, a Web service design phase, a
extremely risky and difficult as Web services can be           Web service implementation phase, and a Web service
relatively simple, like the delivery of a currency converter   validation and testing phase. It recognises the inefficiency
or stock quotes to a cell phone, but also very complex,        of current general-purpose software engineering method-
like a payment processing service where millions of euros      ologies to address successfully Web service engineering
are being transferred in individual transactions from one      matters and proposes a novel Web service creation proc-
account to another.                                            ess based on fundamental object-oriented analysis and
design concepts and on important results of service crea-                                           specification: JWSDL (the Java API for WSDL), JAX-
tion research regarding the development of telematic ser-                                           RPC (the Java API for XML based RPC), JAXM (the
vices upon distributed object platforms utilising SOAs.                                             Java API for XML Messaging), SAAJ (the SOAP with
The novel character of the proposed methodology is rein-                                            Attachments API) and JAXR (the Java API for XML
forced by the adoption of an incremental and iterative use                                          Registries). Although J2EE is an open standard, there are
case driven approach, by the consideration of the special                                           several competing J2EE development environments
needs imposed by the Web Services Architecture, by the                                              (Jboss+Tomcat, BEA WebLogic, IBM WebSphere, Sy-
careful incorporation of the Unified Modelling Language                                             base EAServer). It is evident that due to the increased
(UML) notation and the XML technology throughout the                                                capabilities of these platforms and their continual im-
service creation process, by the exploitation of specially                                          provement the selection process is a challenging task [8].
constructed design patterns, and by the promotion of re-
usability and dynamic Web service compositions.                                                     4. The importance of service grids
                                               - Define Web Service Development Plan
                              Requirements     - Define Web Service Requirements
                               Refinement      - Define Use Cases (high level & essential)
                                               - Define Draft Conceptual Model
                                               - Consider the Application of Rapid Prototyping
                                               - Define Draft Architecture Layers
                                                                                                       A distributed Web services infrastructure will be re-
                Web Service
                Development                                                                         quired before Web services technology can be broadly
                                               - Define Essential Use Cases
                                                                                                    deployed to support mission critical applications within
                  Cycle 1
                               Web Service     - Define Web Service Conceptual Models
 Requirements                   Analysis       - Define Web Service Sequence Diagrams

                                                                                                    and across enterprises. The difference between traditional
 Capture and                                   - Define Web Service Operation Contracts
   Analysis                                    - Define XML Schemas
                Web Service                    - Define Web Service State Diagrams
                  Cycle 2                                                                           Web content and Web services originates from the addi-
                                               - Define Real Use Cases
 Web Service
                               Web Service
                                               - Define User Interface Aspects
                                               - Define Web Service Interaction Diagrams
                                                                                                    tion of process – the sequence of events that need to hap-
                                               - Refine XMLSchemas
                                               - Define Web Service Design Class Diagrams
                                               - Define Web Service Composition Scenarios
                                                                                                    pen in order to produce a result. The fact that the users /
                                                                                                    participants of a Web service are distributed across the
                                                                                                    Web and need to complete certain processes adds
 Web Service                                   - Implement Service Scripts & HTML Code
 Optimisation                  Web Service     - Implement Service Classes & Interfaces
                              Implementation   - Implement Graphical User Interface
                Web Service
                                               - Consider Interworking / Interoperability Matters
                                               - Implement Database Schema
                                                                                                    important new operating requirements, such as con-
                  Cycle n                      - Integrate Implementation Work
                                                                                                    sistency, authenticity, timeliness, integrity, and per-
                               Web Service     - Apply Test Scemes
                                               - Check Web Service Composition Matters
                                                                                                    sistence [6].
                                                                                                       The distributed Web services infrastructure must sup-
                               and Testing     - Consider Artifact Synchronisation

Figure 3. Outline of the proposed Web service                                                       port these requirements. Service grids constitute a key
development methodology                                                                             component of this infrastructure, especially as its scope
    Unlike other SOA systems, Internet middleware does                                              expands beyond the boundaries of the enterprise to en-
not define a specific invocation mechanism. It simply                                               compass a broad range of business partners. Service grids
defines the communication protocols (XML, SOAP, etc).                                               provide a set of enabling utilities and ancillary services to
The specifics of how Web services interact with SOAP                                                support more robust connections between providers and
and WSDL have been left as an exercise to the service                                               users of Web services. This enabling functionality offered
developer’s community. Since the WSA is based on stan-                                              by service grids is distinct from application functionality
dard XML, Web services can be implemented by using                                                  that is directly useful to end-users. It focuses on support-
the pervasive XML processing techniques that are sup-                                               ing the application logic with functionality like security,
ported by a variety of software tools, together with ad hoc                                         routing of messages across Web services or data trans-
invocation implementation patterns. However, efficiency                                             formation so that one Web service can access data from
can be greatly improved by using specialized Web ser-                                               another Web service. It can be considered as the equiva-
vices platforms, which provide a ready-made foundation                                              lent of the supporting functionality provided by object-
for building and deploying Web services, based on a set                                             oriented middleware in SOAs, with the difference that in
of carefully selected invocation mechanisms. The advan-                                             this case it is delivered as a set of managed services,
tage of using a Web services platform is that developers                                            rather than installed in the computing infrastructure com-
don’t need to be concerned with constructing or inter-                                              municating at either end of the connection [5].
preting SOAP messages. They simply write the service                                                   The full value of the proposed framework for the
code (application logic) and rely on the Internet middle-                                           development of Web services is realized when it is used
ware to do the rest.                                                                                in combination with a carefully created service grid in an
    The two most prominent Web services platforms cur-                                              integrated manner. This will also require the enhancement
rently are Microsoft’s .NET and Sun’s J2EE. More spe-                                               of the proposed methodology in order to take into account
cifically, Microsoft has defined a set of standard pro-                                             the availability of the managed services offered by the
gramming interfaces and class libraries for the Visual                                              service grid, especially during the specification of non-
Studio .NET languages within the .NET framework, and                                                functional requirements.
the Microsoft SOAP Toolkit provides support for COM-                                                   Although service grids are still at a very early stage of
based applications written in Visual Basic and Visual                                               development, there is no doubt that the adoption of Web
C++. On the other hand, the Java Community Process’                                                 services technology will be significantly affected by the
(JCP) has recently defined a set of standard programming                                            pace and scope of service grid deployments. Nevertheless,
interfaces for Java Web services, as part of the J2EE                                               significant initiatives are already taking place leading to
the emergence of early generations of service grids and         alternative implementations of this Web service are being
specialized service grid utilities.                             constructed (using Microsoft’s .NET and Sun’s J2EE) and
                                                                special emphasis is placed on Web service composition
5. Conclusions and future work                                  matters, as the training material can originate by a variety
                                                                of providers, and on the incorporation of session tracking,
    Web service engineering provide a sound basis for de-       as the maintenance of state information for the students
veloping and deploying interoperable Web services, al-          by the Web service improves the overall performance,
lowing the gradual transformation of the Internet to a          simplifies program development and provides for a more
global common information networking platform where             intuitive user interface. This validation attempt aims to
organizations and individuals communicate with each             provide tangible evidence about the correctness, the effi-
other to carry out various commercial activities and to         ciency and the true practical value of the proposed meth-
provide value-added functionality. With the emergence of        odology. All these efforts treat the proposed framework as
Web services the Internet has ceased to be solely a con-        a conceptual “umbrella” for Web service engineering
tent transmission network. It has become a computing            activities and gradually transform it to a more precise and
execution network, processing commercial transactions           concrete construct.
and business applications.                                         Web services constitute undoubtfully a promising
    However, many of the standards required for Web             technology that will increasingly assist the integration of
services are not yet fully defined. The SOAP, WSDL and          heterogeneous islands of application logic (objects on the
UDDI specifications that underpin current Web services          Web) to homogeneous component-based solutions (a web
technology form a de facto standard infrastructure with         of objects), especially when supported by robust service
little endorsement by official standards organizations. For     grids. However, developers should keep in mind that Web
this reason, the existing specifications contain a number       services are still a fast moving target and an immature
of ambiguities and inconsistencies, and address only basic      technology. Nonetheless, Web services technology pro-
Web services communications. Two standards groups are           vide the appropriate solution for the agility requirements
currently working on the definition of official Web             that software engineering must cope with today and per-
services standards: The World Wide Web Consortium               haps will encounter increasingly in the future. Existing
(W3C) and the Organisation for the Advancement of               object-oriented middleware such as COM+/.NET,
Structured Information Standards (OASIS). W3C focuses           CORBA, and EJB/RMI may be still necessary to imple-
on core infrastructure specifications and OASIS focuses         ment sophisticated back-end services, but Web services
on higher-level functionality.                                  claim a prominent role when these functionality islands
    In general, Web services computing poses significant        must be connected to fully operational networked
theoretical and engineering challenges as developers de-        systems.
termine how to leverage emerging technologies to auto-
mate semantically rich application domains and to create        References
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                                                                    3, March 2002, pp. 146-154.
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objectives and learning preferences, attend specially de-           Architecture Requirements”, W3C Working Draft, Aug. 19,
signed e-classes that satisfy their needs, participate in           2002[http://www.w3.org/TR/2002/WD-wsa-reqs-20020819].
training multiplayer games that enhance their under-            [8] J. Williams, “The Web Services Debate: J2EE vs. .NET”,
standing and test their knowledge, getting feedback in              Communications of the ACM, Vol. 46, No. 6, June 2003, pp.
order to amend or enrich their learning objectives. Two             59-63.

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