Description Logics with concrete domains present an approach to realize a general engineering workbench. They provide a representation language that enables us to describe in a uniform way devices, assemblies and components along with their structure, constraints on attributes and physical laws as well as models of their correct and faulty behavior. Furthermore, sound and complete algorithms can be given for a set of basic inferences. These basic inferences render it possible to simulate the behavior of the devices and provide the basic building blocks for consistency-based diagnosis. In addition they enable us to devise procedures for finding errors, omissions and inconsistencies in model libraries.