Abstract
Our system OSVIRA (Ontology-Based System for Semantic Information Retrieval Visio-conference and Annotation) is devoted to the development of help to annotation and semantic search of multimedia conferencing resources. It is based on the use of ontology associated with dense thesaurus. It allows using multiple ontology relating to the same seamlessly domain with the ability to define links of equivalence between concepts and / or relationships of different ontology considered. The OSVIRA’ thesaurus besides the uses of uses linguistic relations to reinforce relations between terms and enlarge the semantics of vocabulary. OSVIRA allows to describe semantically the content of a pedagogic multimedia resources on the basis of an intuitive model of annotation based on the triplet {Object, Relation, Object}. It formally represents this content using conceptualgraphs.