Knowledge management has been a major problem in the implemented configuration systems. One rea-son for the difficulties is the complexity of the product descriptions in these systems. The product experts can no longer understand product the way it is described. The problem is addressed in the object-oriented spirit by looking for ways of making the configuration product structure models more com-prehensible. A data model for describing generic product structures is defined. It forms a basis for modelling the evolution of both product configura-tion knowledge and delivered products.