6. Web Services – An Overview

The World Wide Web Consortium (W3C) is responsible for developing interoperable technologies including specification, guidelines, software, and tools for Web-based applications.

The Web is evolving from a pure document repository into a provider of information and computing services. Traditional Web-based systems and services are built on exiting Web server with an integration of technologies using CGI methods and techniques. As the advancement of Web technologies, the Web is used to deliver IT infrastructure, application development, application hosting and service, application maintenance, and end-user software, the standardized programmatic interfaces for remote invocation of software objects among heterogeneous computer systems over the Internet are desired.

Web services is defined as “A Web service is a software application identified by a URI, whose interfaces and binding are capable of being defined, described and discovered by XML artifacts and supports direct interactions with other software applications using XML based messages via internet-based protocols: http://www.w3.org/TR/2002/WD-wsa-reqs-20020429.” In short, a Web service is a programmable application component that is accessible through standard Web protocols and associated technologies.

The W3C charges one coordination group and three working groups with the tasks of developing standard protocols for Web services and applications:

Web Service Coordination Group: http://www.w3.org/2002/ws/cg/
Web Service Architecture Working Group: http://www.w3.org/2002/ws/arch/

Web Service Architecture Requirements: http://www.w3.org/TR/2002/WD-wsa-reqs-20020429
Web Services Architecture Usage Scenarios: http://www.w3.org/TR/2002/WD-ws-arch-scenarios-20020730/

XML Protocol Working Group: http://www.w3org/2000/xp/Group/
Web Service Description Working Group: http://www.w3.org/2002/ws/desc/

Web Service Description Languages (WSDL 1.2): http://www.w3.org/TR/wsdl12/
Web Service Description Usage Scenarios: http://www.w3.org/TR/ws-desc-usecases/
Web Service Description Requirements: http://www.w3.org/TR/ws-desc-reqs/

Web service is expected to play a major role in developing next generation distributed computing systems. It raises a number of challenges in dealing with system’s fault tolerance and reliability:

Atomicity
Consistency
Isolation
Durability

Web Services Advantages

An enabling architecture for wide-area distributed computing among heterogeneous computer systems over the Internet.
Distributed information technology knowledge and data based on the XML standard
Using XML-based languages for developing Web service objects, (collection of data and methods) with predefined interfaces for accessing data and methods.
Remote method invocation

Main Components of Web Services Architecture

As shown in the Figure 1, main components of Web services architecture include:

Web service providers (produce, test, and publish SOAP-based Web services on the Internet)

Service description (WSDL definitions for Web services)

Web service requester (with XML-based SOAP clients based on the WSDL and searching for published services in UDDI directory)
Web service registry (in a centralized UDDI registry)

Open standards:

Web Service Definition Language (WSDL) – an XML-based protocol for describing interface of Web service objects:

Functionality
Interfaces
Uniform Resource Identifier address

Simple Object Access Protocol (SOAP) – an XML-based messaging protocol for information exchange (transporting service requests and responses). SOAP sets rules for how to encode data in XML
Universal Description, Discovery and Integration (UDDI) – a specification or framework defines distributed directory services to the Web service producers and consumers.

Existing platforms that compliant with the Web service architecture are

Microsoft .NET
J2EE (Java 2 Enterprise Edition)

Web Service Applications

Web Services, technology for deploying and providing access to business functions over the Web. Web Service can be implemented without requiring radical rework. Web Service can be introduced incrementally, leveraging existing platforms and languages, to provide enhanced business opportunities and ultimately lower cost. Web Services can provide data interchange and application compatibility information to both business-to-consumer (B2C) and B2B e-business.

From the technology view, how Web Service can address the challenges of B2B process. The difficulty in implementing technologically complex B2B systems is data interchange and remote procedure calls (RPCs). Data interchange presents problems because mapping data formats across vendors and platforms is a daunting task. A change in data format at one location can wreak havoc throughout the system. RPCs pose a different challenge: regardless of the technologies employed or the business function mapped, each process a company wants to automate requires an exercise in specifying and documenting a new RPC. Each new customer requires anew connection, a new construct, and a new complex interface. XML and Web Services address both data interchange and RPC. XML has found its way into a multitude of products and every major platform. Web Service offers a practical solution to the discovery of RPC interfaces. A Web Service is an interface that describes a collection of operations that are network accessible through standardized XML messaging. Web Services can provide access to business processes over the Internet using traditional programming standards, such as HTTP, as well as newer technologies.

Web Service Interoperability Organization (WS-I)

http://xml.coverpages.org/ws-i.html presents an article “Web Service Interoperability Organization (WS-I): [February 07, 2002] IBM and Microsoft, together with an additional fifty-three(+) industry leaders, have formed a new Web Services Interoperability Organization "committed to promoting interoperability among Web services based on common, industry-accepted definitions and related XML standards support. WS-I brings the work of multiple standards development organizations together for the purpose of providing clarity and conformance around Web Services." WS-I working groups will be chartered to produce specific sets of deliverables such as testing tools and sample Web services. These deliverables will be targeted at providing resources to assist Web services developers "to create interoperable Web services, and to verify that their results are compliant with both industry standards and WS-I recommended guidelines." Key deliverables include (1) Profiles, which identify version-specific sets of Web services specifications that interoperate to support specific types of solutions; (2) Sample Implementations exposing interoperability issues; (3) Implementation Guidelines with implementation scenarios, sample solutions, and test cases illustrating compliance verification; (4) A 'Sniffer' tool to monitor and log interactions with a Web service; (5) An 'Analyzer' conformance testing tool which processes sniffer logs to verify that the Web service implementation is error-free. WS-I is open to any organization supporting the goal of interoperable Web services. …. “