Composite objects revisted

In object-oriented systems, an object may recursively reference any number of other objects. The references, however, do not capture any special relationships between objects. An important semantic relationship which may be superimposed on a reference is the IS-PART-OF relationship between a pair of objects. A set of objects related by the IS-PART-OF relationship is collectively called a composite object. An earlier paper presented a model of composite objects which has been implemented in the ORION object-oriented database system at MCC. Although the composite-object feature has been found quite useful, the model suffers from a number of serious shortcomings, primarily because it overloads a number of orthogonal semantics on the references. In this paper, first we present a more general model of composite objects which does not suffer from these shortcomings. Further, [KIM87b] made an important contribution by exploring the use of composite objects as a unit for versions, physical clustering, and concurrency control. The extended model of composite objects necessitates non-trivial changes to the results of [KlM87b]. This paper describes the new results on the use of composite objects as a unit of not only versions, physical clustering and concurrency control, but also authorization.