In P2P data management systems, semantic interoperability between any two peers that do not share the same ontology relyes on ontology matching. The established correspondences, i.e. the “shared” parts of the ontologies are indeed essential to exchange information. But to what extent the “unshared” part can contribute to information exchange. In this paper, we address this question. We focus on a P2P document management system, where documents and queries are represented by semantic vectors. We propose a specific query expansion step at the query initiator's side and a query interpretation step at the document provider's. Through these steps, unshared concepts contribute to evaluate the relevance of documents wrt a given query. The experiments show that the proposed method enables to correctly evaluate the relevance of a document even if concepts of a query are not shared. In some cases, we are able to find up to 90% of the documents that would be selected when all the concepts are shared.