The entity-relationship (E-R) approach is a widely used technique for the semantic modelling of commercial database systems. This paper demonstrates that the E-R method can also be applied in the modelling of static design knowledge for knowledge-based engineering design systems. It presents the basic definitions of the E-R data modelling method and describes some extensions which are useful to model the functionality of system components. It demonstrates the use of this method to produce a generic model of a centrifugal hydraulic pump, which is being used in the implementation of an object-oriented intelligent CAD system. Finally, conclusions on the suitability of the entity-relationship for engineering knowledge representation are drawn.