Abstract : Documentary heritage of firms has often accumulated without that they can adapt to the pace of information technologies' developments. Collective memory ever to be produced sees its mass growing and becomes scattered and heterogeneous. Like many companies, cross-cutting issues today impose the EDF Nuclear Engineering Division (DIN) being able to mobilize its knowledge operationally. But the valuation of its information heritage goes far beyond technical aspects to take into account the organization as a whole. These are indeed the core business of the company which are the starting point of our reflection. In this engineering context the technical knowledge pass through the documentation and is expressed by specific business concepts. The terminology of trades is the key to valorize the knowledge and better manage the patrimony of the DIN. It allows us to go towards an explicit representation, in a knowledge base centered on the "business sense" of the organization. Our approach resolutely empirical and qualitative results in a method of constructing a trades' knowledge base applied to a delimited area of the EDF Nuclear Engineering Division.