This paper deals with some modeling aspects that have to be addressed in the context of the integration of heterogeneous and autonomous XML resources. We propose an integration system, but the emphasis of this paper is neither on its algorithmic aspects nor on its technical details. Instead, we focus on the significance of offering appropriate high-level primitives and mechanisms for representing the semantics of XML data. We posit that support for such primitives and mechanisms is a pre-requisite for realizing the goals of the semantic Web.