Black Cats and Yellow Birds - What do Viewpoint Correspondences Do?

The ODP Reference Model is one of a number of specification frameworks which are based on the definition of a set of viewpoints that are coupled together by the definition of correspondences between terms. Wherever a correspondence is declared, any real world entity that is represented by a term in one viewpoint must also satisfy the requirements placed by the occurrence of the corresponding term in the other viewpoint. Although this idea represents an intuitively simple and satisfying way of talking about the design of complex systems, the idea of a correspondence is not as simple as it might, at first sight, appear. This paper uses simple examples to illustrate some of the complexities resulting from the coupling of object models and examines the consequences for claims of conformance to the complete system of specifications.