Making a configuration of a complex product in the course of a sales process is a difficult matter. A sales-support information system (SSIS) can be a useful help for sales men. An SSIS should give support in two problem areas. The first area concerns the problem of getting a valid product specification, i.e. a specification of a product which falls within the product assortment. The second area concerns the problem of getting the product that is the best solution for the problem of the customer. Such an SSIS must be able to communicate in three different languages. These languages are called user-language, functional language and technical language. In this paper the problem of specifying a product in technical language is treated. With the building of a prototype of such an SSIS it is demonstrated that it is possible to give a salesman sufficient support for the problem of getting a valid product specification. The proposed solution for the second problem area has not been processed into the prototype.