Abstract: OWL-S is a semantic Web service composition-oriented ontology description and semantic markup language that can be explained by the automatic machine,while it also achieved the interoperability of Web service functions between the services,it is one of the most important service portfolio standards. This paper presented a probabilistic model based on non-Markov random PETRI NETS (NMSPN) , which can model and describe the control flow of Web services described in OWL-S. then, the paper established a series of probabilistic analysis methods to achieve a quantitative credibility to analyze the semantics of Web services-based process model based on NMSPN.

Key words: PETRI nets, OWL-S, Web service composition, Service quantitative description models