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Policy-it's more than just security: from just-in-time integration to web services.

Article Excerpt
Business has long pursued the goal of making IT more of a strategic tool and less of a necessary evil. Organizations are constantly looking for easier, cheaper, and more logical ways to build applications and unite the silos of functionality they still depend on. One approach that has met with some success is the concept of just-in-time integration--a technique to combine new functionalities as quickly and cheaply as required, whether they reside inside an organization or outside of it (i.e., with a business partner).

From the architectural perspective, just-in-time integration is a cornerstone of service-oriented architecture (SOA). Under SOA, applications consist of aggregations of calls to services. Services are simply coarsely grained functions that are made available to invoking applications using a consistent semantic. They might encapsulate a well-defined unit of business logic, a legacy application, or an interface to a data gathering system. What a service does is not a concern of SOA--how it is made available is. One of the fundamental principles of SOA is the idea of loose coupling. Loosely coupled systems exhibit a flexibility such that a change effected in one component of the system does not break the rest of the system.

To achieve this, SOAs typically provide a mechanism to publish services and a means for consumers to discover and invoke them dynamically. Web services is an SOA--composed of technologies like SOAR, WSDL, and UDDI--that has the unique characteristic of being based on open standards and being independent of the deployment platform. This is in contrast to other SOAs, such as Sun's Jini, and alternative distributed application technologies, such as OMG's CORBA or Microsoft's COM+. But despite the media triumph of Web services, we still have a long way to go from this basic set of technologies to the end goal of just-in-time integration. This article will explore one of the most important issues in providing true loose coupling in a system of interconnected services.

WSDL Isn't Enough

A fundamental clement in SOA is the interface, or contract. it defines the syntax of a service. It describes an interface by name, what data types the consumer must provide when calling the service, and what a consumer can expect to receive in return. The contract may also describe some service semantics using comments embedded in the description or through the logical grouping of functionality--such as methods or operations--into a common service unit. There is congruency between the SOA contract and the interface...

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