A new approach to product modelling in a design context is proposed. CAD-software must not only enable product modelling, but must also support product design. This is not fully achieved in the traditional'enumerative'approach to product modelling. We discuss how product design and modelling can be based on a facetted'approach to information modelling, and how a data model that supports the design process can be based on a framework for system information. The background for our research is the current development in the construction industry towards a computer integrated construction process. A first prerequisite for this is the use of computer based models. Another prerequisite is that CAD-software can support the design of the results of the construction process, including construction works, user organisations, and the production and facility management processes. A third prerequisite is that computer based models are built with standardised concepts and terminology to enable exchange of information between different actors and computer systems during different stages of the construction process. Principles for organising frameworks for user organisation and construction works information are presented in an appendix