Frameworks for incorporating semantic relationships into object-oriented database systems

A semantic relationship is a data modeling construct that connects a pair of classes or categories and has inherent constraints and other functionalities that precisely reflect the characteristics of the specific relationship in an application domain. Examples of semantic relationships include part-whole, ownership, materialization, and role-of. Such relationships are important in the construction of information models for advanced applications, whether one is employing traditional data modeling techniques, knowledge-representation languages, or object-oriented modeling methodologies. This paper focuses on the issue of providing built-in support for such constructs in the context of object-oriented database (OODB) systems. Most of the popular object-oriented modeling approaches include some semantic relationships in their repertoire of data modeling primitives. However, commercial OODB systems, which are frequently used as implementation vehicles, tend not to do the same. We will present two frameworks by which a semantic relationship can be incorporated into an existing OODB system. The first only requires that the OODB system support manifest type with respect to its instances. The second assumes that the OODB system has a special kind of metaclass facility. The two frameworks are compared and contrasted. In order to ground our work in existing systems, we show the addition of a part-whole semantic relationship both to the ONTOS DB/Explorer OODB system and the VODAK Model Language (VML).