Engineering knowledge is characterized by variant and alternative designs for each problem. To alleviate reuse these variants should be captured as classes in the schema of the engineering database. The resulting class hierarchy may be bloated by intersection classes. This paper proposes a mechanism, called "aspects", which uses a restricted form of multiple instantiation to avoid intersection classes. Unlike similar approaches, such as "roles", our work allows various interdependencies between the different aspects of a class to be modeled. We demonstrate these abilities on an example taken from chemical process engineering.