: The aim of this paper is to present an approach and automated tools for designing knowledge bases describing the contents of information sources in PICSEL2 knowledgediators. We address two problems: the abstraction problem and the representation problem, when information sources are relational databases. In a first part, we present an architectural overview of the PICSEL mediator showing its main knowledge components. Then, we describe our approach and tools that we have implemented (1) to identify, by means straction process, the main relevant concepts, called semantic concepts, in an Entity Relationship model and (2) to help representing these concepts using CARIN, a logical language combining description logics and Datalog Rules, and using specific terms in the application domain model. Key words: information sources modeling, identification of concepts, entity-relationship escription logics, knowledge abstraction, support to knowledge representation.