Virgil Wallentine

Experiences with the portability of concurrent PASCAL

The process of transporting Brinch Hansens implementation of Concurrent PASCAL to another minicomputer is described. Applicable porting strategies are discussed with emphasis on the design decisions made for a specific transportation. Important design decisions include the use of a virtual code interpreter and implementation in an operating system environment. The problems of this transportation are illustrated with accompanying suggestions for a more portable system.

A performance study of the RPE mechanism for PDES

We present the latest implementation of our Remote Process Execution (RPE) mechanism for parallel discrete-event simulation (PDES), along with results of an empirical study of its performance. RPE is an optimistic time warp based mechanism, which allows logical processes on one processor to execute remotely on another when the former is lagging behind in the computation. The advantage is that processors running too far ahead need neither wait, nor run excessively optimistically: they can instead do some useful work for processors which are falling behind. The disadvantage of course, is the cost associated with running processes remotely. The experiments we have run so far show that performance can be significantly enhanced through RPE under the right conditions. In particular, as expected, the site of computation grains was found to be of primary importance. Though our tests were ran with relatively few processors, we suggest a few simple modifications which should allow the scheme to work well for large numbers of computing elements.<<ETX>>

Data access in distributed data base management systems

Abstract A software organization which provides for data definition and manipulation in a distributed data base system is presented by describing the functions and interrelations of the component processes; with its methodology for access, the physical location of the data is transparent to the user program. The concepts of distributed data bases are discussed and current research is summarized as a means of establishing a method for the data placement and location mechanism. Procedures for the movement of data in a distributed data base system are presented, along with the data manipulation procedures, in terms of their performance and integrity effects. Enhancements to the mechanisms are suggested.

DEBL: a knowledge-based language for specifying and debugging programs

This paper describes a knowledge-based language-DEBL which integrates specification and debugging features for distributed programs. It provides programming language independent facilities which makes it adaptable to different programming environments. The semantics of DEBL is based on a temporal logic system which enhances DEBL with rigorous deduction power. The items in the knowledge-base form a hierarchy in which higher level and more complex logical concepts are constructed from lower and simpler ones.