21 February 2011 Por Martin Fowler, disponible en: http://martinfowler.com/bliki/TradableQualityHypothesis.html
I commonly come across developers who are frustrated because "management want more features, they don't care about quality". I'm always sad when I hear this, because when I hear this I know that the developers, management and their customers have alreadylost. Their defeat has been caused by framing the situation in terms of the tradable quality hypothesis. In many aspects of life, quality is something we trade-off for cost. A nicer car will cost more, so we might forego that Ferrari we fancy for something cheaper. Shall I spend the extra for really fresh fish at Turners, or go to the supermarket? As a result we are used to the idea that qualitycosts more. Sometimes we're prepared to pay, sometimes we'll go for the cheaper option. From time to time you'll hear this notion applied to software, particularly software design. Refactoring some crufty code will take time, we'd rather add more features instead. The underlying assumption here is that quality is tradable, by enforcing less quality we gain in the other dimensions of cost, scope, orspeed. When we examine this hypothesis we have to first think about what we mean by quality. Quality means different things to different people. In a software context we might define quality as how pleasing the user-interface is, or how many defects show up, or how well-factored the software is. I follow Kent Beck in making a distinction between internal and external quality. The pleasantness andeffectiveness of a user-interface is external quality as it's something that can be perceived by the users of a system. That is something that can be sensibly involved in a trade off - do I want extra work on making feature A easier to use or should I add feature B? The internal structure of the software, however, is not something that's directly perceivable by the user. I can't tell from using aprogram whether its internals are constructed well or not. Internal quality is thus a more hidden attribute. When someone says we should do things that reduce the design quality of a system to build more features, that person is applying the tradable quality hypothesis to internal quality.
The trouble with doing this, is that if internal quality is tradable, then it makes no sense to put anyeffort into internal quality at all. If a good design stops us from adding features and provides no benefit to the user then why do it? The reason that people care about internal quality is because they think another hypothesis applies - the DesignStaminaHypothesis. In this hypothesis internal quality isn't tradable because reducing internal quality slows us down. It's true that not attending todesign can supply a short term speed up, but this is only over a quite short time horizon - far shorter than most people think. But the tragedy is that as soon as you frame internal quality as tradable, you've lost. People are so used to quality being tradable that even in the best circumstances you're going to have difficulty overcoming it. Saying that we need to spend less time adding new featuresto improve quality is just nailing down the lid. Instead it's vital to focus on the true value of internal quality - that it's the enabler to speed. The purpose of internal quality is to go faster. This cuts both ways, of course, it also means you should understand how putting some time into a refactoring is going to help you go faster, otherwise you shouldn't be doing it. This, by the way, isanother source of disquiet I have with the software craftsmanship metaphor. When you say 'craft' to people, they imagine fine workmanship, leather panelling, smooth joints - and consequently higher costs. The word 'craft' reinforces the tradable quality hypothesis - and that's a crippling disadvantage to those of us who know that speed requires good design.
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