OWL-S plays a key role in describing behaviors of Web services because of potential semantic Web. Although OWL-S has given semantics to concepts by ontology technology, it gives no formal semantic for control-flow and data-flow. Most of previous related research concentrates on model checking instead of providing a precise mathematic semantics for the specification. This gives limitation when properties deal not only with causality of events but also with data types or recursive constructs. This paper presents an algebraic semantics framework for OWL-S sub-set. And data-flow semantics including ldquoPreconditionrdquo, ldquoResultrdquo and ldquobindingrdquo etc are explained too.