Path existence constraints in object-oriented databases

The notion of complex objects by using object identifier as attribute value is one of the typical features in object-oriented database management systems (OODBMSs), which handles the complicated nested structure of objects in the real world. Using this notion, we can navigate in the database among the related objects one after another. Therefore, the notion of reference path in complex objects is a very essential concept in OODBs. However, the integrity constraints for the reference path in complex objects are not discussed enough in formal. In this paper, we propose a notion of path existence constraint definitions (in short, PED) as a method to treat formally the existence dependencies, especially, among object reference paths. By introducing the notion of selector variables, an arbitrary object can be specified as a unit of the path existence constraints. Several inference rules for PEDs are shown, and practical application examples are described in order to show the effectiveness of the notion of PEDs.