Computers are currently used for a large variety of tasks in building design and analysis. Among the basic software types used are 2-D draughting systems, 3-D modelling systems, spreadsheet and database programs, technical calculation and simulation software. One of the major drawbacks in today's situation is that almost every program uses a unique internal representation of the relevant data describing the building to be designed or analyzed. Consequently it is very difficult to exchange data directly between different programs. A new approach to solving this integration problem is to standardize the representation of building data through the use of building product models. A product model structures both the geometrical information traditionally found in drawings and the information about materials, properties etc. found in specifications and bills of materials. The techniques used for structuring product models come from database and knowledge-based systems theory. Basic concepts are entities or objects, attributes describing classes of objects and relationships between different objects. ISO's Standard for the Exchange of Product Data (STEP) will hopefully provide a general product model standard applicable to all sorts of manufactured products, whether buildings, electronic circuits or machine parts. In Finland the basic principles of a product model for buildings (the RATAS-model) have been defined in a national industrywide co-operation project. The widespread use of product model-based software should in the future enable simulation programs to get most of their input data directly from the CAD models of the designers. This, together with better user interfaces, should lower the threshold for using simulation software in everyday design work.