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Java/J2EE, Spring, Linux
viernes, 22 de diciembre de 2017
domingo, 3 de diciembre de 2017
Design by contract (Software engineering, Bertrand Meyer)
1. Design by contract
As object-oriented techniques steadily gain ground in the world of software development. users and prospective users of these techniques are clamof object-oriented or more and more loudly for a “methodology” software construction - or at least for some methodological guidelines.
This article presents such guidelines, whose main goal is to help improve the reliability of software systems. Reliability is here defined as the combination of correctness and robustness or more prosaically, as the absence of bugs.
Everyone developing software systems. or just using them, knows how pressing
this question of reliability is in the current state of software engineering. Yet the
rapidly growing literature on object-oriented analysis, design, and programming
includes remarkably few contributions on how to make object-oriented software
more reliable. This is surprising and regrettable, since at least three reasons justify
devoting particular attention to reliability in the context of object-oriented development:
The cornerstone of object-oriented technology is reuse. For reusable components, which may be used in thousands of different applications, the potential
consequences of incorrect behavior are even more serious than for application specific developments.
Proponents of object-oriented methods make strong claims about their beneficial effect on software quality.
Reliabitity is certainly a central component of any reasonable definition of quality as applied to software.
*The object-oriented approach, based on the theory of abstract data types,
provides a particularly appropriate framework for discussing and enforcing
reliability.
Reliability is even more important in object-oriented programming than elsewhere. This article shows how to reduce bugs by building software
components on the basis of carefully designed contracts.
The pragmatic techniques presented in this article, while certainly not providing infallible ways to guarantee reliability, may help considerably toward this goal. They rely on the theory of design by contract. which underlies the design of the Eiffel analysis, design, and programming language’ and of the supporting libraries, from which a number of examples will be drawn.
The contributions of the work reported below include a coherent set of methodological principles helping to produce correct and robust software; a systematic approach to the delicate problem of how to deal with abnormal cases. leading to a simple and powerful exception-handling mechanism; and *a better understanding of inheritance and of the associated techniques (redeclaration, polymorphism, and dynamic binding) through the notion of subcontract, allowing a systematic approach to using these powerful but sometimes dangerous mechanisms.
Most of the concepts presented here have appeared elsewhere. They were previewed in the book “Object-Oriented Software Construction”; and a more complete exposition was presented in a recent book chapter,”from which this article has been adapted”. More profoundly, this work finds its root in earlier work on systematic program development and abstract data types. This article focuses on the central ideas, introducing them concisely for direct application by developers.
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