الفهرس 
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Abstract
The drastic growth of the Internet, the ongoing developments in hardware . (HlW) and software (S/W) industries, and the recent advances in networking technology have boosted the emergeoce of Information and Communication Technology (ICT). ICT systems enable applications to be divided into components that can be executed on geographically distributed information systems. These applications are commonly referred to as distributed applications. Moreover, distributed computing provides the fundamental technology for the realization of services based enterprise. On the other hand, a service-oriented model of S/W is one in which software functionality is delivered as a service, where each time functionality is required, service elements are identified, terms and conditions are negotiated and then discarded. However, the Quality of Service (QoS) is often a critical factor. For example, unavailability of e-business applications directly leads toloss of revenue rl-13. 511. the issue of trust