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The authors discuss the development of open systems science (OSS) beginning with its roots in the fundamentals of concurrency. The nature of actors., which are the primitives of concurrency, is considered. The aim of OSS is to provide a foundation for effective technological solutions to the complex problems of large-scale open systems by providing a scientific discipline that focuses on issues of robustness, manageability, and scalability. In the large-scale open systems of the future, the focus with shift from centralized systems toward decentralized ones, with an emphasis on conflict processing. The evolution of this paradigm presents some challenges and some fruitful new ideas for distributed artificial intelligence that are discussed.>

This paper is intended as a contribution to analysis of the implications of viewing offices as open systems. It takes a prescriptive stance on how to establish the information-processing foundations for taking action and making decisions in office work from an open systems perspective. We propose due process as a central activity in organizational information processing. Computer systems are beginning to play important roles in mediating the ongoing activities of organizations. We expect that these roles will gradually increase in importance as computer systems take on more of the authority and responsibility for ongoing activities. At the same time we expect computer systems to acquire more of the characteristics and structure of human organizations.

Scientific communities have proven to be extremely successful at solving problems. They are inherently parallel systems and their macroscopic nature makes them amenable to careful study. In this paper the character of scientific research is examined drawing on sources in the philosophy and history of science. We maintain that the success of scientific research depends critically on its concurrency and pluralism. A variant of the language Ether is developed that embodies notions of concurrency necessary to emulate some of the problem solving behavior of scientific communities. Capabilities of scientific communities are discussed in parallel with simplified models of these capabilities in this language.

This paper presents a specification language, implementation mechanism, and proof techniques for problems involving the arbitration of concurrent requests to shared protected resources whose integrity must be preserved. This mechanism is the serializer, which may be described as a kind of protection mechanism, in that it prevents improper orders of access to a protected resource. Serializers are a more structured form of the monitor mechanism of Brinch Hansen and Hoare.

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.

This paper presents a mechanism for the arbitration of parallel requests to shared resources. This mechanism is the serialize, which may be described as a kind of protection mechanism, in that it prevents improper orders of access to a protected resource. The mechanism is a generalization and improvement of the monitor mechanism of Brinch-Hansen and Hoare.Serializers attempt to systematize and abstract desirable structural features of synchronization control structure into a coherent language construct. They represent an improvement in the modularity of synchronization over monitors in several respects. Monitors synchronize requests by providing a pair of operations for each request type [examples are STARTREAD/ENDREAD and STARTWRITE/ENDWRITE for the readers-writers problems]. Such a pair of operations must be used in a certain order for the synchronization to work properly, yet nothing in the monitors construct enforces this use. Serializers incorporate this structural aspect of synchronization in a unified mechanism to guarantee proper check-in and check-out. In scheduling access to a protected resource, it is often desired to wait in a queue for a certain condition before it continues execution. Monitors require that a process waiting in a queue will remain dormant forever, unless another process explicitly signals to the dormant process that it should continue. Serializers improve the modularity of synchronization by providing that the condition for resuming execution must be explicitly stated when a process enters a queue making it it unnecessary for processes to signal other processes. Each process determines for itself the conditions required for its further execution.The behavior of a serializer is defined using the actor message-passing model of computation. Different versions of the "readers-writers" problems are used to illustrate how the structure of a serializer corresponds in a natural way to the structure of the arbitration problem to be solved. The correspondence makes it easier to synthesize a scheduler from behavioral specifications and to verify that an implementation satisfies its specifications.No claim is made for the "completeness" of the serializer mechanism, beyond showing that semaphores can be implemented using serializers. Further, no "complete" solution is proposed to the "no-starvation" specification which requires that a resource reply to each request which it receives. Rather, it is shown for some simple examples that serializers represent a step toward better structuring of parallel access to shared resources, and that proofs that starvation is impossible for these examples are easier with serializers than with some of the currently existing mechanisms for controlling parallel access to resources.

Work on PLANNER-73 and actors has led to the development of a basis for semantics of programming languages. Its value in describing programs with side-effects, parallelism, and synchronization is discussed. Formal definitions are written and explained for sequences, cells, and a simple synchronization primitive. In addition there is discussion of the implications of actor semantics for the controversy over elimination of side-effects.

The PLANNER project is continuing research in natural and effective means for embedding knowledge in procedures. In the course of this work we have succeeded in unifying the formalism around one fundamental concept: the ACTOR. Intuitively, an ACTOR is an active agent which plays a role on cue according to a script. We use the ACTOR metaphor to emphasize the inseparability of control and data flow in our model. Data structures, functions, semaphores, monitors, ports, descriptions, Quillian nets, logical formulae, numbers, identifiers, demons, processes, contexts, and data bases can all be shown to be special cases of actors. All of the above are objects with certain useful modes of behavior. Our formalism shows how all of these modes of behavior can be defined in terms of one kind of behavior: sending messages to actors. An actor is always invoked uniformly in exactly the same way regardless of whether it behaves as a recursive function, data structure, or process.