The service discovery based on semantic description plays an important role in the process of Web Service composition. Traditional approaches to modeling semantic similarity between Web Services compute subsume relationship for function parameters in service profiles within a single ontology. In this paper, we introduce a new graph theoretic framework based on bipartite graph matching for finding the best correspondences among function parameters belonging to advertisement and request. On computing semantic similarity between a pair of function parameters, we present a novel similarity function determining similar entity which relaxes the requirement of a single ontology and accounts for the different ontology specifications.