Inheritance under Participation Constraints

Traditional database systems have been successful in handling large amounts of data but lack mechanisms for schema derivations and schema veriication. In this paper, we propose (i) structures that carry expressive and useful information on the database schema, (ii) a set of inference rules for schema derivations, and (iii) a mechanism for discovering contradictory schema declarations. To this end, in addition to the usual Isa relation, we deene a stronger form of specialization for properties, that we call restriction isa, or Risa for short. The Risa relation expresses property value reenement. A distinctive feature of our model is that it supports the interaction between (explicit or derived) Isa and Risa relations, in diierent contexts. We demonstrate that the combination of Isa and Risa provides a powerful conceptual modeling mechanism. The Risa relation allows to express participation constraints on properties. Speciically, properties of a class are characterized as necessary, possible, or inapplicable on a given subclass. Whether explicitly declared or derived, this information is useful for several reasons: (i) It aids the user to understand better the semantics of the subclass, (ii) it uncovers contradictory declarations or design errors, and (iii) it characterizes property values that are missing from the database. Our data model supports property inheritance, disjoint classes, and negative information (expressed in the form of inapplicable properties). In particular, disjointness, in conjuction with Isa and Risa, can lead to the derivation of negative information or the detection of contradictory declarations .