Polyinstantiation integrity in multilevel relations

Polyinstantiation integrity (PI) as defined in the Sea View multilevel relational data model consists of a functional dependency component and a multivalued dependency component. It is shown that the latter component rules out many practically useful relations and is therefore unduly restrictive. This leads the authors to propose that PI be defined to consist only of the functional dependency component. For this revised definition of PI, they formulate and prove correct a lossless decomposition of multilevel relations into single-level ones with recovery based on the natural join operation