PREFACE Analysis,design and implementation It is always risky to use a notation that externally looks like a programming language,as this may suggest that it only covers the implementation phase.This impression,however wrong,is hard to correct,so frequently have managers and developers been told that a gap of metaphysical proportions exists between the ether of analysis-design and the underworld of implementation. Well-understood object technology reduces the gap considerably by emphasizing “SE.AMLESSNESS the essential unity of software development over the inevitable differences between levels AND REVERSIBIL- of abstraction.This seamless approach to software construction is one of the important ITY",28.6.page 930. contributions of the method and is reflected by the language of this book,which is meant for analysis and design as well as for implementation. Unfortunately some of the recent evolution of the field goes against these principles, through two equally regrettable phenomena: Object-oriented implementation languages which are unfit for analysis,for design and in general for high-level reasoning. Object-oriented analysis or design methods which do not cover implementation(and are advertized as "language-independent"as if this were a badge of honor rather than an admission of failure). Such approaches threaten to cancel much of the potential benefit of the approach.In contrast,both the method and the notation developed in this book are meant to be applicable throughout the software construction process.A number of chapters cover high-level design issues;one is devoted to analysis,others explore implementation techniques and the method's implications on performance. The environment Software construction relies on a basic tetralogy:method,language,tools,libraries.The method is at the center of this book;the language question has just been mentioned.Once in a while we will need to see what support they may require from tools and libraries.For obvious reasons of convenience,such discussions will occasionally refer to ISE's object- oriented environment,with its set of tools and associated libraries. The environment is used only as an example of what can be done to make the The last chapter.36. concepts practically usable by software developers.Be sure to note that there are many summarizes the other object-oriented environments available,both for the notation of this book and for environment. other O-O analysis,design and implementation methods and notations;and that the descriptions given refer to the state of the environment at the time of writing,subject,as anything else in our industry,to change quickly-for the better.Other environments,O- O and non O-0,are also cited throughout the text.x PREFACE Analysis, design and implementation It is always risky to use a notation that externally looks like a programming language, as this may suggest that it only covers the implementation phase. This impression, however wrong, is hard to correct, so frequently have managers and developers been told that a gap of metaphysical proportions exists between the ether of analysis-design and the underworld of implementation. Well-understood object technology reduces the gap considerably by emphasizing the essential unity of software development over the inevitable differences between levels of abstraction. This seamless approach to software construction is one of the important contributions of the method and is reflected by the language of this book, which is meant for analysis and design as well as for implementation. Unfortunately some of the recent evolution of the field goes against these principles, through two equally regrettable phenomena: • Object-oriented implementation languages which are unfit for analysis, for design and in general for high-level reasoning. • Object-oriented analysis or design methods which do not cover implementation (and are advertized as “language-independent” as if this were a badge of honor rather than an admission of failure). Such approaches threaten to cancel much of the potential benefit of the approach. In contrast, both the method and the notation developed in this book are meant to be applicable throughout the software construction process. A number of chapters cover high-level design issues; one is devoted to analysis; others explore implementation techniques and the method’s implications on performance. The environment Software construction relies on a basic tetralogy: method, language, tools, libraries. The method is at the center of this book; the language question has just been mentioned. Once in a while we will need to see what support they may require from tools and libraries. For obvious reasons of convenience, such discussions will occasionally refer to ISE’s object￾oriented environment, with its set of tools and associated libraries. The environment is used only as an example of what can be done to make the concepts practically usable by software developers. Be sure to note that there are many other object-oriented environments available, both for the notation of this book and for other O-O analysis, design and implementation methods and notations; and that the descriptions given refer to the state of the environment at the time of writing, subject, as anything else in our industry, to change quickly — for the better. Other environments, O￾O and non O-O, are also cited throughout the text. “SEAMLESSNESS AND REVERSIBIL￾ITY”, 28.6, page 930. The last chapter, 36, summarizes the environment