Extensional and Intensional Strategies

This paper is a contribution to the theoretical foundations of strategies. We first present a general definition of abstract strategies which is extensional in the sense that a strategy is defined explicitly as a set of derivations of an abstract reduction system. We then move to a more intensional definition supporting the abstract view but more operational in the sense that it describes a means for determining such a set. We characterize the class of extensional strategies that can be defined intensionally. We also give some hints towards a logical characterization of intensional strategies and propose a few challenging perspectives

Proving Temporal Properties of Concurrent Programs: A Non-Temporal Approach

This thesis develops a new method for proving properties of concurrent programs and gives formal definitions for safety and liveness. A property is specified by a property recognizer - a finite-state machine that accepts the sequences of program states in the property it specifies. A property recognizer can be constructed for any temporal logic formula. (ABRIDGED ABSTRACT

Key Exchange Using Keyless Cryptography

Protocols to generate and distribute secret keys in a computer network are described. They are based on keyless cryptography, a new cryptographic technique where information is hidden by keeping only the originator of a message, and not its contents, secret

Verifying Temporal Properties without using Temporal Logic

An approach to proving temporal properties of concurrent programs that does not use temporal logic as an inference system is presented. The approach is based on using Buchi automata to specify properties. To show that a program satisfies a given property, proof obligations are derived from the Buchi automaton for that property. These obligations are discharged by devising suitable invariant assertions and variant functions for the program. The approach is shown to be sound and relatively complete. A mutual exclusion protocol illustrates its application

Proving Boolean Combinations of Deterministic Properties

This paper gives a method for proving that a program satisfies a temporal property that has been specified in terms of Buchi automata. The method permits extraction of proof obligations for a property formulated as the Boolean combination of properties, each of which is specified by a deterministic Buchi automaton, directly from the individual automata. The proof obligations can be formulated as Hoare triples. The method is proved sound and relatively complete. A simple example illustrates applica- tion of the method

Defining Liveness

A formal definition for liveness properties is proposed. It is argued that this definition captures the intuition that liveness properties stipulate that "something good" eventually happens during execution. A topological characterization of safety and liveness is given. Every property is shown to be the intersection of a safety property and a liveness property

The Myth of Scalable High Performance

ral. Sparse matrix problems are parameterized by the dimensions of the matrix as well as by the number of nonzeros. Sorting problems may be parameterized by the range (and distribution) of the keys as well as by the number of items to be sorted. Thus, performance landscapes may sit in spaces with three or more independent variables. Agreeing on the cuts through such spaces that give appropriate scalability graphs may not be worth the effort. Assuming that the methodological problems could be overcome, the main advantage of scalability analysis is that it allows comparison of algorithms without regard to the ratio of communication cost to computation cost. If one algorithm is scalable and a second isn't then, for any fixed (or increasing) ratio, there is some number of processors beyond which the scalable algorithm is always better. However, from the point of view of the performance programmer [AC94], this information gives no insight into which algorithm one should use on any specifi

Message Compression for High Performance

this paper