An OODB part-whole model: Semantics, notation and implementation

摘要

The notion of a part-whole relationship plays an important role when modeling data in many advanced application domains. It is therefore important that Object-Oriented Database (OODB) systems include support for this modeling primitive. We present a comprehensive part model for OODB systems. The model's foundation is a part-whole relationship that captures a variety of real-world, part-whole semantics, partitioned into four characteristic dimensions: exclusiveness, multiplicity, dependency and inheritance. These impose constraints on any ‘part’ transactions (like ‘add-part’) to ensure that the state of the database remains consistent with the prescribed part-whole semantics. They also provide functionality like deletion dependency and several kinds of inheritance, both from the part to the whole and vice versa. The part relationship gives flexibility to an application developer who simply declares the desired semantics and then lets the OODB system automatically enforce it. We also introduce a graphical notation that can be used to express the enhanced semantics in the development of OODB part-whole schemata. Our part model has been integrated into the VODAK Model Language (VML), an OODB system, with the use of its extensible metaclass mechanism.