The paper proposes an alignment framework for a set of domain ontologies in order to enable their interoperability in a number of information retrieval tasks. The procedure starts by anchoring the domain ontologies concepts to the concepts of a generic reference ontology. This allows the representation of each domain concept as a fuzzy set of reference concepts or instances. Next, the domain concepts are mapped to one another by using fuzzy sets relatedness criteria. The match itself is presented as a fuzzy set of the reference concepts or instances, which allows the comparison of a new ontology directly to the already calculated matches. The paper contains a preliminary evaluation of the approach