Loretta Guarino Reid

Thesis Title: Control and Communication in Programmed Systems
Degree Type: Ph.D. in Computer Science
Advisor(s): Nico Habermann
Graduated: December 1980

Abstract:

The paper "On the Duality of Operating Systems Structures" by Lauer and Needham (1978) was an extremely controversial paper. It claimed to have demonstrated an important result about communication in operating systems, but it left many people uneasy and unsure of exactly what had been demonstrated. Attempts to formalize the results of the paper by casting it in terms of known models of systems failed, primarily because the models lacked the ability to represent the dynamic nature of systems.

A model of communication, consisting of primitive objects and communication operations, is developed in this thesis in order to study communication properties of systems. Some of the goals of the design of the model were to permit us to deal with the dynamic creation and destruction of pieces of systems, to permit the description of systems programmed in a wide variety of languages and implemented on a wide range of architectures, and to provide some support for flexibility and the localization of communication knowledge in systems.
Although the primitives of the model are sufficient to describe communication in systems, working with them directly is much like programming only with GO TOs. There is a lot of structure to the way that communication takes place, and this structure is not explicitly visible in the use of the primitives. The thesis introduces a notation for describing abstract communication constructs in a way that permits the structure to be expressed precisely and that allows constructs to be compared for their similarities and differences.

The thesis uses the model and the notion of abstract communication constructs to explore several issues in communication. In an effort to characterize the properties of communication that make it easy to use programs in many different systems, the criterion of the flexibility of an implementation is developed. The Lauer-Needham paper is discovered not to demonstrate the duality of the two types of operating systems but to introduce an abstract communication construct that is flexible enough to be implemented directly in both systems. Finally, a proof is given of the necessary and sufficient conditions on communication for a system to be completely sequential.

Thesis Committee:
Nico Habermann (Chair)

Nico Haberman, Head, Computer Science Department