Stanley Letovsky

Delocalized Plans and Program Comprehension

A maintainers understanding can go awry when it is based on purely local clues. How can we spell out the intentions behind a piece of code?

Mental models and software maintenance

Abstract Understanding how a program is constructed and how it functions are significant components of the task of maintaining or enhancing a computer program. We have analyzed vidoetaped protocols of experienced programmers as they enhanced a personnel data base program. Our analysis suggests that there are two strategies for program understanding, the systematic strategy and the as-needed strategy. The programmer using the systematic strategy traces data flow through the program in order to understand global program behavior. The programmer using the as-needed strategy focuses on local program behavior in order to localize study of the program. Our empirical data show that there is a strong relationship between using a systematic approach to acquire knowledge about the program and modifying the program successfully. Programmers who used the systematic approach to study the program constructed successful modifications; programmers who used the as-needed approach failed to construct successful modifications. Programmers who used the systematic strategy gathered knowledge about the causal interactions of the programs functional components . Programmers who used the as-needed strategy did not gather such causal knowledge and therefore failed to detect interactions among components of the program.

CPROP : a rule-based program for constructing genetic maps

Gene mapping assigns chromosomal coordinates to genetic loci based on analysis of fragmentary ordering and metric data. In assembling genetic maps, geneticists use rules of inference to derive new facts about order and distance between loci from experimentally derived conclusions about order and distance. They construct comprehensive maps by merging related sets of data and resolving conflicts between them. In this article we describe software that formalizes and automates some of these rules of inference to yield a useful map construction utility called CPROP.

A program anti-compiler

A description is given of CPU, a program analysis tool that converts programs into formal specifications. CPU takes as input a program plus a knowledge base of programming plans and finds instances of plans in the code. A technique called transformational analysis is used in which plans that are recognized in the code are replaced by descriptions of their goals. Both procedural plans and data-structuring plans can be recognized. The result of a transformational analysis is a hierarchical derivation of the program, where the topmost layer constitutes a formal specification for the input program, the bottommost layer is the original code, and the intermediate layers denote plans that were recognized in the program. This derivation can be used to generate summaries of the code and to answer questions about it.<<ETX>>

CPROP: A RULE-BASED PROGRAM FOR CONSTRUCTING GENETIC MAPS

Gene mapping assigns chromosomal coordinates to genetic loci based on analysis of fragmentary ordering and metric data. In assembling genetic maps, geneticists use rules of inference to derive new facts about order and distance between loci from experimentally derived conclusions about order and distance. They construct comprehensive maps by merging related sets of data and resolving conflicts between them. In this article we describe software that formalizes and automates some of these rules of inference to yield a useful map construction utility called CPROP.