The Globus toolkit (GT) is the de facto open source toolkit for Grid computing. The functionality of the GT version 3.x is exposed as a collection of virtual Open Grid Services Architecture services . OGSA services, or Grid services, extend Web Services, discussed in the previous chapter, to add features that are often needed within distributed applications. Specifically, OGSA adds state to Web Services in order to control the remote service during its lifetime. Whereas Web Services are stateless, OGSA-based services are stateful. OGSA services represent the GT's various components, e.g., GRAM, MDS, etc., described in Chapter 9, using this unified representation and can be aggregated and used within virtual organizations in a number of different ways.
However, the road to OGSA realisation has not been easy. In 2002 the Open Grid Services Infrastructure specification was announced. This specification defined the extensions to WSDL needed in order to represent and enable stateful Web Services. The designers of OGSI introduced the notion of a Grid service, which extended a basic Web Service to attach a number of additions to which a Grid service must adhere. Stateful resources within OGSI were modelled as Web Services that support the GridService portType (see Section 16.2.2), which is an extension of the WSDL portType.
KeywordsGrid Service Service Instance Virtual Service Globus Toolkit Open Grid Service Architecture
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