Software to publish, from time to time, articles cut from a different mold. This is one in that series. The object of the CONTROVERSY CORNER articles is both to present information and to stimulate thought. Topics chosen for this coverage are not just traditional formal discussions of research work; they also contain ideas at the fringes of the field’s “conventional wisdom.”

An investigation was made of the characteristics of computer programming languages intended for the implementation of provably correct programs and of the characteristics of programs written in these languages. It was discovered that potential run time exceptions and the necessity of providing a rigorously correct implementation of exception handlers so dominate the potential control paths of programs written in verifiable languages that the usual code optimization techniques are ineffective. It was further discovered that the call intensive control structures of these programs, necessitated by verification constraints, also thwart optimization and lead to inefficient code. It is shown that theorems can be derived at potential exception sites which, if true, guarantee that the exception condition will never arise permitting removal of the exception path from the program’s flow graph. These theorems are proved using the automatic theorem prover which is part of the program verification system. Is is also shown that many of the routine calls contained in verifiable programs may be reduced in expense by converting parameters to global variables or eliminated completely by expanding the called routines at their call sites. Both the exception suppression and call reduction techniques reduce the complexity of the program’s call graph and facilitate conventional optimizations. Several examples are presented and the potential improvements in code size resulting from the application of these techniques are discussed.

I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. Components are widely seen by software engineers as an important technology to address the “software crisis”. An important aspect of components in other areas of engineering is that system reliability can be estimated from the reliability of the components. We show how commonly proposed methods of reliability estimation and composition for software are inadequate because of differences between the models and the actual software systems, and we show where the assumptions from system reliability theory cause difficulty when applied to software. This thesis provides an approach to reliability that makes it possible, if not currently plausible, to compose component reliabilities so as to accurately and safely determine system reliability. Firstly, we extend previous work on input sub-domains, or partitions, such that our

This paper examines a number of successful requirements engineering efforts carried out by the author and determines that a critical element in the success of these efforts was the author's ignorance of the client's domain.

It is the intention of the Journal of Systems and Software to publish, from time to time, articles cut from a different mold. This is one in that series. The object of the CONTROVERSY CORNER articles is both to present information and to stimulate thought. Topics chosen for this coverage are not just traditional formal discussions of research work; they also contain ideas at the fringes of the field’s “conventional wisdom.” This series will succeed only to the extent that it stimulates not just thought, but action. If you have a strong reaction to the article that follows, either positive or negative, write to Robert L. Glass, Editor,