Semantic Web Services facilitate activities including automatic discovery and composition of Web Services. Research initiatives such as WSMO have been developing specifications for this technology. This paper describes a model for composition of Web services. The proposed model complements the WSMO orchestration in IRS-III, a framework for Semantic Web Services based on WSMO specification. We present a tool based on the above model that supports a user-guided interactive composition approach, by recommending component Web services according to the composition context.