Specifications in a Data Independent Accessing Model

The Data Independent Accessing Model (DIAM) Project of the Information Sciences Department of IBM Research is directed towards developing an architectural basis for an advanced data base system - a data base system which, in addition to providing advanced functional capabilities and a new level of data independence, is not limited either in the access paths which can be declared (in order to support the user-specified information collections) or in the encodings which are possible for those access paths. We have already been presented with a general overview of the basic system (1). In that overview, DIAM was seen to be composed of 4 basic levels of description: the Entity Set Model the String Structure Model the Encoding Model the Physical Device Model. In this paper we shall concentrate on the middle two of these levels - the String Structure and the Encoding Models.