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D. L. Parnas

Research and Advances Jan 1 1983

A technique for software module specification with examples

This paper presents an approach to writing specifications for parts of software systems. The main goal is to provide specifications sufficiently precise and complete that other pieces of software can be written to interact with the piece specified without additional information. The secondary goal is to include in the specification no more information than necessary to meet the first goal. The technique is illustrated by means of a variety of examples from a tutorial system.

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Author Archives

Research and Advances Mar 1 1975

On a solution to the cigarette smoker’s problem (without conditional statements)

This report discusses a problem first introduced by Patil, who has claimed that the cigarette smoker's problem cannot be solved using the P and V operations introduced by Dijkstra unless conditional statements are used. An examination of Patil's proof shows that he has established this claim only under strong restrictions on the use of P and V. These restrictions eliminate programming techniques used by Dijkstra and others since the first introduction of the semaphore concept. This paper contains a solution to the problem. It also discusses the need for the generalized operators suggested by Patil.
Computing Applications
Research and Advances Dec 1 1972

On the criteria to be used in decomposing systems into modules

This paper discusses modularization as a mechanism for improving the flexibility and comprehensibility of a system while allowing the shortening of its development time. The effectiveness of a “modularization” is dependent upon the criteria used in dividing the system into modules. A system design problem is presented and both a conventional and unconventional decomposition are described. It is shown that the unconventional decompositions have distinct advantages for the goals outlined. The criteria used in arriving at the decompositions are discussed. The unconventional decomposition, if implemented with the conventional assumption that a module consists of one or more subroutines, will be less efficient in most cases. An alternative approach to implementation which does not have this effect is sketched.
Research and Advances May 1 1972

A technique for software module specification with examples

This paper presents an approach to writing specifications for parts of software systems. The main goal is to provide specifications sufficiently precise and complete that other pieces of software can be written to interact with the piece specified without additional information. The secondary goal is to include in the specification no more information than necessary to meet the first goal. The technique is illustrated by means of a variety of examples from a tutorial system.
Research and Advances Oct 1 1971

Concurrent control with “readers” and “writers”

The problem of the mutual exclusion of several independent processes from simultaneous access to a “critical section” is discussed for the case where there are two distinct classes of processes known as “readers” and “writers.” The “readers” may share the section with each other, but the “writers” must have exclusive access. Two solutions are presented: one for the case where we wish minimum delay for the readers; the other for the case where we wish writing to take place as early as possible.

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