Database Instances, Abstract Data Types and Database Specification

We present in this report a method of database specification which overcomes a severe drawback of most database models and specification techniques – namely the inability to formalise the concept of database instance (state). The lack of formalisation of this concept in a model results in the inability to present a uniform treatment of queries and updates. We indicate why previous models and specification techniques are inadequate in this respect and then develop a modelling technique to overcome this situation. The use of algebraic specification tools in conjunction with this technique is illustrated in the specification of an example database.