The MAOUSSC (Model for Assistance in the Orientation of a User within Coding Systems) Web server supports a collaborative work on the description of medical procedures. The specifications for the MAOUSSC application are conceptual modeling, definition of semantically fully described procedures, re-use of an existing vocabulary, the UMLS, and sharability. This paper reports on some difficulties in applying those principles in a networked building and updating of the terminology. The users are physicians who have to represent procedure terms in the MAOUSSC formalism. They must apply the constraints of the underlying model, and re-use the representation of the UMLS knowledge base. In our experience, we found that the implementation of syntactic and semantic constraints was not sufficient. Guidelines for pragmatical aspects in representation are required to make a collaborative approach in terminology building more operational.