A Graphical Data Modelling Program with Constraint Specification and Management

Semantic data models are intended to be tools with which database applications can be designed in a relatively intuitive way by a permitting a description of the database which is close to its meaning. For the most part, however, such tools only permit the structure of the data to be described, whereas much of the meaning of the model of data required by the application can only be expressed as constraints. This paper describes how an implementation of the IFO data model has been extended to allow some categories of constraint to be captured. In doing so, constraints become values in the metadata which are therefore amenable to a number of different uses. In order to explore the implications of the work, the paper discusses various issues, including the role of constraints, how they may be specified and how they may be managed.