Integrating A Part Relationship Into An Open OODB System Using Metaclasses

Abstract

The part-whole semantic relationship (the part relationship, for short) is an important modeling primitive in many advanced application domains such as manufacturing, design, and document processing. In this paper, we examine the problem of integrating such a construct into an OODB system. Specifically, two questions are addressed in this regard. This first is: Can a part relationship be made an intrinsic construct of an existing OODB system without having to rewrite a substantial portion of the system? The second: Can an “open” OODB system which claims to support such an integration really do so, and, more specifically, can the integration be done using a metaclass mechanism which purports to bring extensibility to the VODAK Model Language (VML)? To demonstrate that both questions can be answered “yes,” we introduce and discuss the details of a custom VML metaclass—the “HolonymicMeronymic” metaclass—which we have built. This metaclass comprises two items, an “instance” type and an “instance-instance” type. Together, the two endow the classes of a part hierarchy and their instances with structure and behavior consistent with our comprehensive part relationship model and the notions of “part” and “whole.” Complete descriptions of each of these two aspects of the metaclass are presented and their effect on schema construction and database usage is discussed.