Constraint specification on object-oriented databases

The main semantics of constraints pertaining to OO (object-oriented) databases are identified, constraints are classified into types based on these semantics, and a simple and powerful constraint language for OO databases is described. If a set of constraints needs to be defined over the same subdatabase, the approach allows for defining the shared subdatabase first, followed by the set of constraints. If the original database is updated causing new extensional patterns to enter into the subdatabase (because they, after the update, satisfy the conditions used to define the subdatabase), these patterns have to satisfy all the constraints specified for the database. Typical database constraints, such as the non-null and total participation constraints, can be easily specified in the language as constraints on patterns of object associations. The implementation of the constraint processing system is described. The language supports the use of the existential and universal quantifiers