Service Oriented Computing

There has been an increase in interest recently within the Grid community towards "Service Oriented'' Computing.Services are often seen as a natural progression from component based software development, and as a means to integratedifferent component development frameworks. A service in this context may be defined as a behaviour that is provided by a component for use by any other component based on a network-addressable interface contract (generally identifying some capability provided by the service). A service stresses interoperability and may be dynamically discovered and used. According to the "Open Grid Services Architecture" (OGSA) framework, the service abstraction may be used to specify access to computational resources, storage resources, and networks in a unified way. How the actual service is implemented is hidden from the user through the service interface. Hence, a compute service may be implemented on a single or multi-processor machine -- however, these details may not be directly exposed in the service contract. The granularity of a service can vary -- and a service can be hosted on a single machine, or it may be distributed. The "TeraGrid'' project provides an example of the use of services for managing access to computational and data resources. In this project, a computational cluster of IA-64 machines may be viewed as a compute service, for instance -- hiding details of the underlying operating system and network. A developer would interact with such a system using the GridSDK toolkit, derived from Globus, and consisting of a collection of services and software libraries.

Web Services provide an important instantiation of the Services paradigm, and comprise infrastructure for specifying service properties (in XML -- via the Web Services Description Language (WSDL) for instance), interaction between services (via SOAP), mechanisms for service invocation through a variety of protocols and messaging systems (via the Web Services Invocation Framework), support for a services registry (via UDDI), tunnelling through firewalls (via a Web Services Gateway), and scheduling (via the Web Services Choreography Language). A variety of languages and support infrastructure for Web Services has appeared in recent months -- although some of these are still specifications at this stage with no supporting implementation. Web Services play an important role in the Semantic Web vision, aiming to add machine-processable information to the largely human-language content currently on the Web. A list of publicly accessible Web Services (defined in WSDL) can be found at www.xmethods.net. By providing metadata to enable machine processing of information, the Semantic Web provides a useful mechanism to enable automatic interaction between software -- thereby also providing a useful environment for agent systems to interact. For the works with Web Services in WeSC, please visit: Experience with Web Services for more information.

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