ROVER: A Framework for the Evolution of Relationships

Relationships have been repeatedly identi ed as an important object-oriented modeling construct. Today most emerging modeling standards such as the ODMG object model and UML have some support for relationships. However while dealing with schema evolution, OODB systems have largely ignored the existence of relationships. We are the rst to propose comprehensive support for relationship evolution. A complete schema evolution facility for any OODB system must provide (1) primitives to manipulate all object model constructs; (2) and also maintenance strategies for the structural and referential integrity of the database under such evolution. We hence propose a set of basic evolution primitives for relationships as well as a compound set of changes that can be applied to the same. However, given the myriad of possible change semantics a user may desire in the future, any pre-de ned set is not suÆcient. Rather we present a exible schema evolution framework which allows the user to de ne new relationship transformations as well as to extend the existing ones. Addressing the second problem, namely of updating the schema evolution primitives to conform to the new set of invariants, can be a very expensive re-engineering e ort. In this paper we present an approach that de-couples the constraints from the schema evolution code, thereby enabling their update without any re-coding e ort.