Building an information server, specific to a given domain, over distributed and heterogeneous informaiton sources, is based on knowledge describing the server domain, called domain ontology. We address the issue of representing such ontologies in the framework of the PICSEL research project. Two steps are described. The first one is directed by the representation formalism and the functionalities of the information server. The second one aims at refining and optimizing knowledge obtained in step one. It is guided by the way functionalities of the server are implemented. The examples in the paper are coming from the tourism products domain.