Decomposing relationship types by pivoting and schema equivalence

In the relational data model, the problem of data redundancy has been succe ssfully tackled via decomposition. In advanced data models, decomposition b y pivoting provides a similar concept. Pivoting has been introduced by Bisk up, Menzel and Polle, and used for decomposing relationship types according to a unary non-key functional dependency. Our objective is to study pivoti ng in the presence of cardinality constraints which are commonly used in se mantic data models. For this, we generalize the notion of pivoting such tha t decomposing relationship types does no longer require the existence of a given unary functional dependency. In order to ensure the equivalence of th e given schema and its image under pivoting, the original application-depen dent constraints have to be preserved. We discuss this problem for sets of participation and co-occurrence constraints. In particular, we prove the ne cessity of path cardinality constraints, and give an appropriate foundation for this concept. (C) 2001 Published by Elsevier Science B.V.