UNIT 2 - GRID SERVICES (1).pdf

A practical view ogsa aims at addressing

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A PRACTICAL VIEW OGSA aims at addressing standardization (for interoperability) by defining the basic framework of a grid application structure. The OGSA standard defines what grid services are, what they should be capable of, and what technologies they are based on. It is called an architecture because it is mainly about describing and building a well-defined set of interfaces from which systems can be built, based on open standards such as WSDL. The objectives of OGSA are Manage resources across distributed heterogeneous platforms Support QoS-oriented Service Level Agreements (SLAs). Define open, published interfaces and protocols for the interoperability of diverse resources. Exploit industry standard integration technologies
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OGSI document consists of specifications on how work is managed, distributed, and how service providers and grid services are described. The Web services component is utilized to facilitate the distribution and the management of work across the grid. WSDL provides a simple method of describing and advertising the Web services that support the grid’s application. Summarizing these observations, OGSA is the blueprint, OGSI is a technical specification, and Globus Toolkit is an implementation of the framework. OGSA describes and defines a Web-services-based architecture composed of a set of interfaces and their corresponding behaviors to facilitate distributed resource sharing and accessing in heterogeneous dynamic environments.
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OGSA relies on the definition of grid services in WSDL, which, as noted, defines, for this context, the operations names, parameters, and their types for grid service access. Based on the OGSI specification, a grid service instance is a Web service that conforms to a set of conventions expressed by the WSDL as service interfaces, extensions, and behaviors. Because the OGSI standard is based on a number of existing standards (XML, Web services, WSDL), it is an open and standards-based solution. The grid service interface is described by WSDL, which defines how to use the service. A new tag, gsdl , has been added to the WSDL document for grid service description. The UDDI registry and WSIL document are used to locate grid services. The transport protocol SOAP is used to connect data and applications for accessing grid services.
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The interfaces of grid services address discovery, dynamic service- instance creation, lifetime management, notification, and manageability. The standard interface of a grid service includes multiple bindings and implementations. Grid services, such as the ones just cited, can, therefore, be deployed on different hosting environments, even different operating systems.
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