An extended universal instance data model

摘要

The universal instance (UI) data model is extended to include the semantic notion of generalization as well as specialization. It is shown how this extension gives the model significantly more modelling capability and overcomes the well-known limitations of other UI models. In particular, the extended model allows both multiply defined attributes and multiple independent relationships. Consequently, the extended UI model has the modelling capability of ER-diagrams, together with the capability to handle nonnavigational (i.e. attribute-based) queries. The semantics of both the standard and extended UI models are also studied, and it is shown that UI models have an unexpectedly rich semantics. Finally, some comparisons with object-oriented models are made. The extended UI model is a purely value-oriented model, but it appears to parallel object-oriented models closely. Some consequences of this similarity are discussed.