A data abstraction approach to database modelling

Abstract

Attempts have been made for some time to reconcile the notions of data base modelling and data abstraction. Considering the overlapping concepts of information hiding and encapsulation from the data abstraction world, and data independence from the database world, it should not be necessary to design yet another programming language as others have done, specialized to a particular data model. Instead, the starting point for our work has been the proposition that an extant general purpose language providing data abstractions should be able to accommodate the popular data models by serving both as a data definition and manipulation language. The criticism has been made that while abstract data types hide the representation details, they also suppress the semantic structure of the data. While this may be true for “programming in the small” [2], it is not the case for “programming in the large” [2]. We will briefly indicate how a CLU-like language [4] (hereafter called XPLS) with minor extensions, plus its supporting module interconnection language (hereafter called the External Structure) can be used as a data-base definition and manipulation language. XPLS has been designed as a front end to PL/I and is supported by a preprocessor to the PL/I compiler. It turns out that XPLS plus External Structure supports and meshes more smoothly with a semantic data model (for example: [1], [3],[5], [6]) than with the older data models. Our work differs from a number of recent specialized languages which exploit data abstractions and strong type checking but which are based on the relation as a primitive data type. Our approach is not based on any particular data model.