||In this paper we discuss the requirements for an information system for product design and present an information system in the form of a prototype computer program that tests these principles in the context of building design.Design is a product determination process, i.e. the properties of a possible product are determined during the process. Design can be categorised as routine or innovative. In routine design the product is well known and the determination process includes selecting a prototype solution and determining its variable attributes. Innovative design is necessary when no such prototype solution can be applied, and new kinds of things and new uses for known things have to be created. Innovative design is a search process characterised by adding and removing attributes from the product model.In an information system for routine design the product model can be an instance of a specific product type, whereas in innovative design the product model must be an instance of a much more generic thing. In the latter case, the classification of the product model is determined successively during the design process.Information systems can be characterised as open or closed concerning classification of model objects, and concerning definition of classes in the conceptual schema. An information system for routine design can be closed in both respects, while an information system for innovative design must be open in these respects, so that the designer can define new attributes and classes and reclassify model objects. Building design, especially during early stages, is an example of innovative design.In the paper we describe a prototype program for product design, with examples of its use in the construction context. The prototype supports the above-mentioned dual openness by implementing a data model where the product model may freely be given attributes and be classified on the basis of these attributes.