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The semantic Web is an extension of the current Web in which information is given well-defined meaning, aiming for machine-understandable Web resources. OWL-S is an ontology language for describing web services in terms of their inputs, outputs, preconditions, effects and their process model. There is a need for formal modeling and analyzing techniques and tools for reliable web services and their composition because of dynamic and complex service composition process. Petri nets are well suited for capturing flows in web services, for modeling the distributed nature of web services, for representing methods in a web service and for reasoning about the correctness of the flows. We use an extended weighted timed Petri net to model and analyze the semantic Web service described by OWL-S. In order to reduce the complexity of model, we use hierarchical Petri nets to model four basic structures of the Web service composition. We propose a definition of reachable service graph and give an algorithm for constructing the reachable service graph of extended weighted timed Petri net. Finally, we discuss the correctness and time and cost performance of the Web service composition by analyzing the reachable service graph.