We address in this paper the issue of a semantic interoperability between systems relying on semantically heterogeneous models, having been designed for the purpose of independent specific goals and activities. Examples of models include ER-schema, ontologies and taxonomies. In our approach, we make explicit the semantics embedded in UML class diagrams. Towards the high expressiveness of UML constructs, we formalize their semantics in terms of a logic belonging to Description logics. However, in our opinion, Description logics?s constructors are not sufficient to express contextual knowledge, we propose a reference metamodel that offers contextual primitives.