Composition of Web services is a cornerstone step in the development of interoperable systems. However, Web services still face data-heterogeneity challenges, although several attempts of using semantics. In addition, the context in which Web services evolve is still somehow "ignored", hampering their adaptability to changes in composition situations. In this paper, we argue how context permits to determine the semantics of interfaces that Web services expose to third parties. We show the need for a context- and semantic-based approach for Web services composition.