| The grid infrastructure is mainly concerned with the creation, management, and the application of dynamic coordinated resources and services. These dynamic and coordinated resources and services are complex. They may be individual or a collection of entities with a short or long lifespan. These resources may be constituted from single or from multiple institutions so as to provide a homogeneous or heterogeneous set of functionalities. Even though the complexity and difference in resources and services may vary within every virtual organization, they are all agreed to deliver a set of QoS features including common security semantics, workflow, resource management, problem determination, failover, and service-level management. These QoS features require a well-defined architecture to achieve the desired level of service quality. This prompted for the introduction of Open Grid Service Architecture (OGSA) to support the creation, maintenance, and application of ensembles of services maintained by virtual organizations (VO) (Foster, Kesselman, & Tuecke). Clarification of the Usage of Resource and Service In most of the technology papers and specifications, the definition of the term "resource" and "service" are used interchangeably to represent anything that is sharable and/or can be used by an external user . Even though this may look conceptually correct for the specific scenarios they may be representing, for our discussion we would like to further clarify the resource and service concepts. A resource is something sharable or a representation of a logical or physical entity (e.g., software application, hardware, operating system, cluster, etc.) and has a number of interfaces or application provider interfaces (API) to mange, access, and monitor the resource. A service is a realization of one of the interfaces with the necessary binding and message exchange pattern information for the use of the client. This is represented in Figure 6.1. Figure 6.1. Relationship between resource and service.  |
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