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3.9 Interoperability

SOA and Web services promise significant benefits: reduced cost and complexity of connecting systems and businesses, increased choice of technology suppliers leading to reduced cost of technology ownership, and increased opportunities for businesses to interact both with customers and suppliers in new and profitable ways. The fundamental premise of Web services is that standardization, predicated on the promise of easy interoperability, resolves many of the long-standing issues facing businesses today. However, Web services and the SOAs that are based upon them are an emergent market. As such, the technologies and specifications that various organizations are defining for Web services are in flux. Issues relate to ambiguity of interpretation of specifications or standards, in addition to differences and insufficient understanding of interactions between them. For Web services to be successful, these specifications must be able to truly provide interoperability in a manner that is conducive to running a business or producing products that can effectively leverage Web services technology. The IT leaders behind the Web services specifications realize that interoperability is in the best interests of all industry participants. In 2002, they created the Web Services Interoperability Organization (WS-I).

3.9.1 WS-I

WS-I [WSI] is an open industry organization that is chartered to promote Web services interoperability across differing platforms, operating systems/middleware, programming languages, and tools. It works across the varied existing industry and standards organizations to respond to customer needs by providing guidance and best practices to help develop Web service solutions. Membership of WS-I is open to software vendors of all sizes, to their customers, and to any others who have interests in Web services. The work of WS-I is carried out by the members in WS-I working groups, generally consisting of individuals who have a diverse set of skills (developers, testers, business analysts, and so on). Members can actively participate in one or more WS-I working groups, based on their specific interest or expertise.

WS-I was formed specifically for the creation, promotion, and support of generic protocols for interoperable exchange of messages between Web services. Generic protocols are protocols that are independent of any actions necessary for secure, reliable, and efficient delivery. Interoperable in this context means suitable for and capable of being implemented and deployed onto multiple platforms. Among the deliverables that WS-I is creating are profiles, testing tools, use case scenarios, and sample applications.

A profile consists of a list of Web services specifications at specified version levels, along with recommended guidelines for use, or the exclusion of inadequately specified features. WS-I is developing a set of profiles that support interoperability. Profiles facilitate the discussion of Web service interoperability at a level of granularity for those people who have to make investment decisions about Web services and in particular Web services products. WS-I focuses on compatibility at the profile level. To avoid confusion, it is likely that only a few profiles will be defined. There is already a consensus on those standards that form the most basic Web services profile, and it is likely—although not mandatory—that as additional profiles emerge, they will indeed be based on this basic profile. In addition to references to industry standards and emerging specifications, a profile might contain interoperability guidelines that can resolve ambiguities. Such guidelines constrain some of the specifications or standard MAYs and SHOULDs, often the source of interoperability problems, such that they become MUSTs or MUST NOTs to satisfy the requirements of the use cases and usage scenarios. The first, or Basic, WS-I profile pertains to the most basic Web services, such as XML Schema 1.0, SOAP 1.1, WSDL 1.1, and UDDI 2.0.

The testing tools monitor and analyze interactions with and between Web services to ensure that exchanged messages conform to the WS-I profile guidelines. Sample applications are being developed to demonstrate the implementation of applications that are built from Web Services Usage Scenarios, which conform to a given set of profiles. Implementations of the same sample application on multiple platforms, using different languages and development tools, allow WS-I to show interoperability and provide readily usable resources for Web services developers and users.

WS-I is committed to building strong relationships and adopting specifications developed by a wide array of organizations, such as the Internet Engineering Task Force (IETF), Open Applications Group (OAGi), OASIS, OMG, UDDI, W3C, and many others. These organizations serve the needs of a vast range of communities and customer bases. It is the plan of WS-I to engage these groups and work together to meet the needs of Web services developers and customers.

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