Modelling database views with derived classes in the UML/OCL-framework

Abstract

One of the central notions in database modelling is the notion of a database view. A database view closely corresponds to the notion of derived class in UML. This paper will show how the notion of a relational database view can be correctly expressed as a derived class in UML/OCL (version 2.0). A central part of our investigation concerns the generality of our manner of representing relational views in OCL. Since, in general terms, a database view closely corresponds to the notion of a named query, an important problem that we address in our paper is the expressiveness of OCL as a query language. In particular, we will discuss the relational completeness of OCL (w.r.t the relational algebra). We will show that OCL (version 2.0) is relationally complete in a minimal sense, but not in a (desired) maximal sense. As a consequence, we will argue for certain language extensions in OCL in order to achieve that OCL is maximally relationally complete. © Springer-Verlag Berlin Heidelberg 2003.