According to conceptual changes on design methodology, this paper presents some research results on a new generation of CAD systems. This new software has not to be used to achieve automatic design tasks at all. On the contrary, it has to make part of an integrated design environment. A co-operative design modeller is then presented as a support for co-operative and integrated design methodology in this design environment. It mainly allows every design actors to share a unique database owing to a formal exchange network. The modeller provides a graphic interface to add, edit or modify data. Moreover the modeller manages the shared database in order to realise heavy design tasks as data propagation or data coherence management. The presented modeller takes place in the global design environment connected to specific applications based on specific design tasks (process planning, structure analysis). An informal communication network worthwhile in any design group including human actors also assists the co-operative design modeller.