This work may not be copied or reproduced in whole of part for any commercial purpose. Permission to copy in whole or part without payment of fee is granted for nonprofit educational and research purposes provided that all such whole or partial copies include the following: a notice that such copying is by permission of the Labor für Künstliche Intelligenz, Hamburg, Germany; an acknowledgement of the authors and individual contributors to the work; all applicable portions of this copyright notice. Copying, reproducing, or republishing for any other purpose shall require an agreement with Labor für Künstliche Intelligenz. Abstract Compared with frame-based systems, description logics have the advantage of well-deened semantics and powerful inferences. In order to exploit these advantages in technical domains, the ability to use concrete domains is needed, e.g. systems of (in)equalities over (non)linear polynomials to handle physical laws. Existing systems can only cope with comparisons between attributes. We present an approach that considerably improves the expressiveness of the concrete domains. Ctl 1 is based on the ideas presented in 1] and 5]. Concrete domains are realised through a well-deened interface to external algorithms. Constraint Logic Programming (CLP) systems allow us to easily realise a whole range of concrete domains, e.g. over sets of symbols and numbers. In particular, we are able to handle systems of arbitrary linear polynomials. They also enable us to automatically participate in recent and future improvements in the areas of CLP and computer algebra, e.g. systems capable of handling arbitrary non-linear polynomials.