666 ON METHODOLOGY $19.2 company then has to pick up the pieces and do the hard work;sometimes the analyst's work turns out to be totally useless as it has missed some of the most important practical constraints.An"analysis only"approach belies the fundamental ideas of seamlessness and reversibility,the integrated lifecycle that characterizes object technology,where analysis and design are interwoven with implementation and maintenance.Someone who misses part of this picture is not equipped to give methodological advice. Reuse Having played a key part in some large projects is necessary but not sufficient.In the object-oriented field the Practical Basis precept yields a corollary:the need for practical reusability experience. Among the distinctive properties of the method is its ability to yield reusable components.No one can claim to be an expert who has not produced a reusedO-O library; not just components claimed to be reusable,but a library that has actually been reused by a substantial number of people outside of the original group.Hence the next precept: Reuse Experience methodology principle To claim expert status in the object-oriented field,one must have played a key role in the development of a class library that has successfully been reused by widely different projects in widely different contexts. A typology of rules Next we should turn to the form of methodology rules.What kind of advice is effective in software development methodology? A rule may be advisory (inviting you to follow a certain style)or absolute (enjoining you to work in a certain way),and it may be phrased in a positive form(telling you what you should do)or in negative form(telling you what you should not do).This gives four kinds: Classification of methodological rules ·Absolute positive:“Always do a”, ·Absolute negative:Never use b”. ·Advisory positive::s“Use c whenever possible'”. ·Advisory negative:“Avoid d whenever possible”. The requirements are slightly different in each case. Absolute positives Rules of the absolute positive kind are the most useful for software developers,since they provide precise and unambiguous guidance.666 ON METHODOLOGY §19.2 company then has to pick up the pieces and do the hard work; sometimes the analyst’s work turns out to be totally useless as it has missed some of the most important practical constraints. An “analysis only” approach belies the fundamental ideas of seamlessness and reversibility, the integrated lifecycle that characterizes object technology, where analysis and design are interwoven with implementation and maintenance. Someone who misses part of this picture is not equipped to give methodological advice. Reuse Having played a key part in some large projects is necessary but not sufficient. In the object-oriented field the Practical Basis precept yields a corollary: the need for practical reusability experience. Among the distinctive properties of the method is its ability to yield reusable components. No one can claim to be an expert who has not produced a reused O-O library; not just components claimed to be reusable, but a library that has actually been reused by a substantial number of people outside of the original group. Hence the next precept: A typology of rules Next we should turn to the form of methodology rules. What kind of advice is effective in software development methodology? A rule may be advisory (inviting you to follow a certain style) or absolute (enjoining you to work in a certain way); and it may be phrased in a positive form (telling you what you should do) or in negative form (telling you what you should not do). This gives four kinds: The requirements are slightly different in each case. Absolute positives Rules of the absolute positive kind are the most useful for software developers, since they provide precise and unambiguous guidance. Reuse Experience methodology principle To claim expert status in the object-oriented field, one must have played a key role in the development of a class library that has successfully been reused by widely different projects in widely different contexts. Classification of methodological rules • Absolute positive: “Always do a”. • Absolute negative: “Never use b”. • Advisory positive: “Use c whenever possible”. • Advisory negative: “Avoid d whenever possible