Local Referential Integrity

This paper introduces the concept of local referential integrity according to which an object may only reference objects belonging to the same composite object. For example, in production planning an employee of some department may only be scheduled to work on machines belonging to the same department. Usually, such a constraint must be stated explicitly by a predicate as \add on" to a database schema. Object-oriented data models have become popular for just the opposite. They represent implicitly integrity constraints which formerly had to be stated explicitly. Prominent examples, which so far have been studied independently, are referential integrity and composite objects. Local referential integrity combines both concepts by applying referential integrity within a composite object. We show that local referential integrity can be represented easily within an object-oriented database schema by using \local object classes" as domains of relationships. A local object class is a set of objects belonging exclusively to some composite object. Local referential integrity is maintained if any relationship from within a composite object to one of its local classes references a current member of that class.