One of the most promising approaches to database support of engineering applications is the concept of object-oriented database management. Object-orientation is usually approached from either a behavioral or structural viewpoint. The former emphasizes the application-specific manipulation of technical objects while hiding their structural details whereas the latter concentrates on the structural aspects and their efficient implementation. The thesis of the paper is that the two viewpoints may enter into a fruitful symbiosis where a behaviorally object-oriented system is implemented on top of a structurally object-oriented database system, thereby combining ease of use by the engineer with high database system performance. The thesis will be demonstrated in the paper by a user-friendly interface based on user-definable abstract datatypes and its implementation using a prototype for the non-first-normal-form (NF2) relational model, and will be supported by an engineering example application from off-line robot programming.