No abstract

The purpose of the present paper is to reconsider the problem of stimulus equivalence (SE). Primary emphasis is placed on the related areas of stimulus generalization, transposition, and discrimination learning as examples of SE. Recent evidence has indicated that the only comprehensive approach to SE, the Hull-Spence system, is inadequate to account for many phenomena in these areas. A theory of SE based on a combination of information and adaptation-level concepts is proposed as an alternative to the Hull-Spence theory. A number of investigations were conducted in order to test certain assumptions of the proposed theory. The results of these studies seem to provide rather striking support for the approach presented in this paper. A main advantage of the proposed theory is that the use of adaptation-level (AL) concepts permits quantitative predictions when an appropriate mathematical model for the calculation of AL is available. It is felt, however, that both in lieu of and in addition to quantitative predictions, that the present system has considerable heuristic value that may stimulate further research.

No abstract

Abstract. Software architecture addresses the high level specification, design and analysis of software systems. Formal models can provide essential underpinning for architectural description languages (ADLs), and formal techniques can play an important role in analysis. While formal models and formal analysis may always enhance conventional notations and methods, they are of greatest benefit when they employ tractable models and efficient, mechanisable techniques. The novelty in our work has been in the effort to find and mechanise a general semantic framework for software architectures that can provide tractable models and support architectural formal analysis. The resultant semantic framework is a layered one: the core is a simple model of the elements and topology, which provides the basis for general architectural theorems and proof techniques; the structural core is augmented by semantic layers representing the semantics of relevant properties of the design. The model has been implemented in the higher-order logic proof tool PVS, and has been used in correctness proofs during a case study of a distributed transaction protocol.

Abstract:The theory of Timed Transition Systems developed by Henzinger, Manna, and Pnueli provides a formal framework for specifying and reasoning about real-time systems. In this paper, we report on some preliminary investigations into the mechanization of this theory using the HOL theorem prover.We review the main ideas of the theory and describe how it has been formally embedded in HOL. A graphical notation of timed transition diagrams and a real-time temporal logic for requirements have also been embedded in HOL using the embedding of timed transition systems. The proof rules proposed by Henzinger et al have been verified formally and we illustrate their use, as well as some problems we have encountered, by reference to a small example. More work is required on interfaces and proof methods to have a generally usable system.