Coordination using Object Attributes

The development of the idea of coordination languages, as deened by Carriero and Gelernter 8], has enabled work in concurrency to abstract away from the internals of processes or agents and hence to focus on their external interactions. A variety of practical parallel and/or distributed systems have resulted from the application of the coordination language concept | the most widely-known of these being Linda 7] and its variants. All coordination systems involve a number of logically shared objects, which may themselves be structures containing further objects. In the context of Linda, these objects are: tuple spaces, which are bags of tuples each consisting of ordered sequences of atomic elements (in some variants, elements can be non-atomic objects). Tuple spaces are shared between concurrent processes which then coordinate (asynchronously) by depositing tuples in, or associatively retrieving tuples from the tuple spaces. However, in thèclassical' Linda model, there are no access properties or similar attributes associated with the objects (tuple spaces, tuples, and tuple elements). This paper addresses the opportunities for, and eeects of, incorporating object attributes | primarily those concerned with access-control, but including examples of some less familiar attributes | in Linda-like tuple-space systems. The focus is on exploring how the coordination properties are aaected by this enhancement, and investigating in what ways the classical Linda model needs to be modiied. Particular emphasis is placed on the potential practical gains to be expected in both performance, and expressibility, with consideration being given to methods for implementing attribute frameworks in open distributed systems.