Hewitt, C.

Modelling Distributed Systems


Distributed systems are multi-processor information processing systems whichdo not rely on the central shared memory for communication. The importanceof distributed systems has been growing with the advent of "computer networks"of a wide spectrum: networks of geographically distributed computers at one end,and tightly coupled systems built with a large number of inexpensive physicalprocessors at the other end. Both kinds of distributed system are made availableby the rapid progress in the technology of large-scale integrated circuits. Yetlittle has been done in the research on semantics and programming methodologiesfor distributed information processing systems.Our main research goal is to understand and describe the behaviour of suchdistributed systems in seeking the maximum benefit of employing multi-processorcomputation schemata.Hayes, J.E., D. Michie, and L. I. Mikulich (Eds.), Machine Intelligence 9, Ellis Horwood.

Viewing control structures as patterns of passing messages


In this way we hope eventually to develop a framework adequate for the discussion of the central issues of problem-solving involving parallel versus serial processing and centralization versus decentralization of control and information storage. This paper demonstrates how actor message passing can be used to understand control structures as patterns of passing messages in serial processing. The ability to analyze or synthesize any kind of control structure as a pattern of passing messages among the members of a society provides an important tool for understanding control structures. Ultimately, we hope to be able to characterize various control structures in common use by societies in terms of patterns of passing messages.

Description and theoretical analysis (using schemata) of PLANNER, a language for proving theorems and manipulating models in a robot


Abstract: PLANNER is a formalism for proving theorems and manipulating models in a robot. The formalism is built out of a number of problem-solving primitives together with a hierarchical multiprocess backtrack control structure. Under BACKTRACK control structure, the hierarchy of activations of functions previously executed is maintained so that it is possible to revert to any previous state. In addition PLANNER uses multiprocessing so that there can be multiple loci of control over the problem-solving.