The Design of an Object-Role Database Management System
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Abstract:
Number: 165 In many class-based object-oriented database systems the association between an instance and a class is both exclusive and permanent. Therefore, these systems have serious difficulties in representing objects taking on different and multiple roles over time. Recently, some researchers have proposed the use of roles to tackle these problems. In their approaches, objects acquire additional properties by dynamically playing roles. However, relationships between objects and roles have not been addressed. Therefore, an object may evolve on its own by dynamic acquiring new roles, without coordination or cooperation by any other objects. In this paper, a novel object-oriented database management system, called DOOR, which supports object evolution, dynamic role (context-dependent) modeling, objects of multiple specific classes, and object-role relationships, is described. In DOOR, a role is an entity with state and behavior, but does not have globally unique identity. Therefore, its existence has to be associated with an object. It acts as a special association between its owner and player, such that its owner can prescribes its state and its player gains its properties through dynamic role playing. In this way, an object can evolve dynamically and cooperatively according to its associating objects. Furthermore we discuss some interesting features of roles which have been seldom addressed. They include playing multiple roles of the same type, player change (or role migration), role ownership and playership, and player-class constraint, etc. We show by examples that all these features are very useful for applications in which objects take on different and multiple roles over time. Part of this work has been done when the authors are visiting the Computer Science Department at UCLA.
