A significant motivation for programming language research is to find good abstractions and conceptual frameworks that enable us to understand and re* son about, certain kinds of complex computational phenomena in a simple way.In this paper we show that the specification of programs for the detection of stable properties of networks of communicating processes is facilitated -almost trivialized -in the framework of concurrent logic programming languages.We present the embedded short-circuit pr* gramming technique for detecting stable properties of networks, and illustrate its utility by providing a simple algorithm for distributed termination detection.We show that, the runtime behavior of a concurrent logic program incorporating this technique (for diffusing computations) is similar to the "DSA" scheme described in [7] for maintaining distributed counters.We modify the technique for repeated detection of quiescence for phased computations such as discrete simulations.We show that the abstraction can be mit nipulated without reference to its implementation by presenting a simple solution to the distributed knotdetection problem [IS].Finally we show that, under certain conditions, a simple extension allows repeated (live) snapshots [3] of the state of the computation to be taken almost trivially, thus providing another technique for detecting stable properties.

Concurrent Prolog supports object-oriented programming with a clean semantics and additional programming constructs such as incomplete messages, unification, direct broadcasting, and concurrency synchronization [Shapiro 1983a]. While it provides excellent computational support, we claim it does not provide good notation for expressing the abstractions of object-oriented programming. We describe a preprocessor that remedies this problem. The resulting language, Vulcan, is then used as a behicle for exploring new variants of object-oriented programming which become possible in this framework.

Knowledge bases built in object-oriented systems use networks of interconnected objects in their representations. The mechanism described here provides a way to use such a network as a prototype by making virtual copies of it. The virtual copy is created incrementally. Values of instance variables in the virtual copy are inherited from the prototype until locally overridden in the copy, similar to inheritance of defaults between instances and classes in Loops. A virtual copy preserves the topology of the original network. Virtual copies can be made from virtual copies. Alternative implementations of virtual copies allow different tradeoffs in space and lookup time. Virtual copies can be used for building knowledge bases for design, for representing contexts in a problem solving system, and have other uses in ordinary programming.

Dynamic computer graphics is best represented as several processes operating in parallel. Full parallel processing, however, entails much complex mechanism making it difficult to write simple, intuitive programs for generating computer animation. What is presented in this paper is a simple means of attaining the appearance of parallelism and the ability to program the graphics in a conceptually parallel fashion without the complexity of a more general parallel mechanism. Each entity on the display screen can be independently programmed to move, turn, change size, color or shape and to interact with other entities.