Web services are becoming de facto a standard for data exchanging, since they provide a clear way to express and access information throughout the Internet. Sometimes, one service alone is not able to perform a certain task, and it might be necessary to compose two or more services in order to accomplish that task. In this context, semantic web services play an essential role, since they provide a framework to formally describe services in a way that it is possible to machines to automatically

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... iscover, compose, invoke, and monitor them. On the other hand, only functionality is not enough to fulfill users' satisfaction, in the sense that service providers should guarantee the quality delivered by their services. In this paper, we present an infrastructure for dynamic web service composition. The main element of the infrastructure is the composition mechanism which is based on quality of service. Experimental results indicates the proposal soundness. Related Work In this section, we discuss a selected set of recent relevant works related to our proposal. In [20] , a middleware for QoS-based web service composition was proposed. It finds the optimal set of service