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Predicative programming Part II
Part I of this two-part paper presented a new semantics of programs. Each program is considered to be a predicate, in a restricted notation, that specifies the observable behavior of a computer executing the program. We considered a variety of notations, including assignment, composition (semicolon), deterministic choice (if), nondeterministic choice, definition (nonrecursive and recursive), and variable declaration. We did not consider any input or output notations, or concurrency; that is the subject of Part II. We assume the reader is familiar with Part I, so that we can build on ideas presented there.
Online help systems: a conspectus
Users of computer systems are now accustomed to the convenience of online help systems and generally demand these amenities in the computers they buy. However, recent studies as to the efficacy of certain types of assistance for certain classes of users raise important questions for designers.
The coordinated use of five performance evaluation methodologies
Information system design can be influenced and ultimate performance parameters accurately forecast through the coordinated use of five performance analysis tools. The complementary methodology is used to first predict and then validate system performance throughout its life cycle.
Is Ada too big? A designer answers the critics
Many have criticized the Department of Defense's new computer language, Ada, saying it is too large, too complicated, or too difficult to use. Are they right? And are there some simplifications that could be made to Ada without destroying its usefulness?
Predicative programming Part I
Programs are given a new semantics with the merit that a specification written as a first-order predicate can be refined, step by step, to a program via the rules of Predicate Calculus. The semantics allows a free mixture of predicate and programming notations, and manipulation of programs.
The operational versus the conventional approach to software development
The conventional approach to software development is being challenged by new ideas, many of which can be organized into an alternative decision structure called the “operational” approach. The operational approach is explained and compared to the conventional one.
Some negative results concerning prime number generators
Programs attributed to Wirth and Misra for generating the prime numbers up to a specified limit are investigated. It is shown that Wirth's program is incorrect according to three increasingly weak criteria, and a composite number is exhibited that the program accepts as prime. This is the smallest known counterexample, and could not have been found by the usual method of program testing—the program would run for trillions of years on the fastest computer before reaching it! Closely related counterexamples are given to a conjecture of Misra concerning his program. An appendix gives a particularly simple algorithmic proof of the Chinese remainder theorem.
Why students reject engineering teaching careers
Many of the country's brightest engineering students have been passing up graduate school for the challenge and high salaries of industry. This is drying up the supply of new Ph.D.s interested in teaching at a time when U.S. engineering schools are struggling to cope with swelling enrollments and a severe faculty shortage.
Assessing software maintainability
How easy is it to maintain a program? To a large extent, that depends on how difficult the program is to understand. A technique to measure program difficulty yields encouraging results.
Congress tackless computer abuse
Congress has been taking an active interest in protecting information stored in computers. Congressional investigations and media reports have highlighted the vulnerability of computer systems to abuse and mis-use. Recent accounts of “system hackers” describe young students and others who gain illegal access to systems, thereby obtaining information and services, as well as disrupting systems.
Software errors and complexity: an empirical investigation0
An analysis of the distributions and relationships derived from the change data collected during development of a medium-scale software project produces some surprising insights into the factors influencing software development. Among these are the tradeoffs between modifying an existing module as opposed to creating a new one, and the relationship between module size and error proneness.
Requirements analysis for Ada compilers
A Guide to the Selection and Specification of Ada Compilers was recently produced by the Portability Working Group of Ada-Europe. Most of the points addressed are applicable criteria for evaluation of any language compiler.
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