When building a knowledge and documents management system, it is often considered that an "ontology" (i.e. a consensual model of the domain) is needed. As a matter of fact, in expert domains (humanities, medical care, engineering, law...), we can find several contradictory "ontologies". Moreover, these conflicting "viewpoints" result in a debate which is the sign of a sense making activity. This does not mean that a domain is not built on a background knowledge, or that there are no media to record this knowledge on. But how do experts use these media throughout their activities? May we say that becoming an expert is like moving away from a beacon?