Semantics of data bases: The semantics of data models

摘要

The definition of data equivalence depends on a notion of the semantics (i.e. the meaning) of the data stored in a data base. To define the semantics of these data it is very important to distinguish between the things to be modelled in a data base and the language in which they are represented. We introduce an abstract data model which is suited to express the semantics of schemas respectively data instances. To represent this model we propose a logical data definition language (LDDL) and a logical data language (LDL) which as a consequence allow to specify the kind of information which may be stored in the data base and which ensures the correctness and consistency of this information.