Inheritance under Participation Constraints and Disjointness

Traditional database systems have been successful in handling large amounts of data but lack mechanisms for schema derivations and schema veri cation 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 de ne a stronger form of spe cialization for properties that we call restriction isa or Risa for short The Risa relation expresses property value re nement A distinctive feature of our model is that it supports the interaction between explicit or derived Isa and Risa relations in di erent 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 Speci cally properties of a class are characterized as necessary possible or inapplicable on a given sub class 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 con tradictory 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