||Even at the very beginning of the use of computers in architecture there had already been the vision to use the new medium for more than just copying the draught man's way of work [l]. Thus, the search for such a computer assisted or even computer automated de- sign process, either for the more artistic or for the more constructive part of the architectural design process, has lasted as long as the history of CAD in architecture itself This search follows different concepts, which are, with more or less intenseness, AI approaches. The more artistic and creative aspects are to be solved by, e.g., Shape Grammar or Case Based Reasoning, the more constructive aspects by Expert Systems. These are approaches on a very high and demanding level. It is still not clear, how far the progress will lead to usability in practice. A more pragmatic but surely arduous approach is to built next generation CAAD system on the basis of a product model. The product model, however, will be a sound foundation for using case based or expert system approaches in a further step of the development. The Next CAAD project follows this approach. The model defines and describes the architectural design objects, their relations, dependencies and constraints. This will be done in a stepwise manner. A stepwise approach is also followed for the handling of dependencies and constraints. In a first phase the user will have to set the rules. In next phases small rule based modules will be taken over as far as they are proved useful.