Abstract. Relation between texts and formal knowledge representations is not straightforward. On the one hand a text cannot be reduced to a formal representation of its content whatever it is, on the other hand a text needs always external knowledge (which eventually may be formalized) in order to be fully interpreted. Moreover relation between text and knowledge is a dynamic one, new texts often carry new knowledge, thus formal representations of knowledge are seldom definitive and has to be continuously updated. In this article we tackle this dynamic aspect of the relation between text and ontology. The aim is not so much to define how to extract ontology from texts but to describe a general framework which compare corpora of text and existing ontology in order to improve ontology quality or characterization of corpuses of texts. We will present a set of metrics in order to compute similarities and differences in sets of corpuses, a tool based on this metrics and primary results obtained with this tool.