In computer science, ontologies were originally used in artificial intelligence in order to share knowledge among applications. The main cited definition of ontology is that of Gruber stating "an ontology is an explicit specification of a conceptualization". A terminological concept represents the normalised meaning of a term through a definition in natural language. The definition states the necessary and sufficient conditions for the term to be associated to its correct denotation. The ontologies described are used in information retrieval systems (IRS) to normalize the vocabulary used to index the content of documents and queries. Ontologies in IRS make it possible to take into account synonyms and hierarchical relations in order to enhance the retrieval process. Data providers share their data on the Web in order to enable unknown applications to discover them and reuse them. Their data schema is composed of several ontologies already published on the Linked Open Data (LOD) in order to improve interoperability.