The design of design, part 3



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Posted by: stak
Tags: design, books
Posted on: 2011-01-04 22:26:34

A few final notes on The Design of Design. In Chapter 10, Brooks talks about the "budgeted resource" (i.e. the resource that is the most constrained) when designing something. One of the things he mentions here is the use of "surrogates" - something is used as an approximation for the actual budgeted resource, since the actual budgeted resource is hard to measure. This is basically the same thing I called an "indicator" in an earlier post; he says the same thing I said, but I like the way he says it better. I also like the word "surrogate" more than "indicator", since the connotations are more in line with the idea it expresses.

In Chapter 11, on constraints, he talks about how adding constraints can help narrow the scope of the project and make it easier to come up with a good design. He specifically cites programming language design as an example - a special-purpose language is easier to design well compared to a general-purpose language. This reminded me of an article on language-oriented programming that I read a while ago. The article claims that LOP allows the programmer more freedom of expression, which makes sense. Since LOP allows the programmer to more losslessly express their mental model, it allows for a better design and implementation. (This ties into yesterday's post on mental models).

Another interesting point in the book is in Chapter 15, where he talks about how disciplines have become increasingly specialized, resulting in a greater separation between design, implementation, and use. As an example, he cites how Henry Ford built his own car, but today no computer engineer can physically make his own chips. I think this same thing happens on a smaller scale for individual products as well. When I first worked at RIM as a co-op in 2003, all the employees had a BlackBerry, and used the devices extensively. The designers and implementers were also users, and the process of dogfooding was one of the reasons the devices worked so well.

Today, all the employees still have and use their devices, but something has changed. Specifically, the user market RIM is targeting is no longer the same, and so the employees are no longer representative of the user population. Dogfooding now still helps, but not nearly as much as it used to, since the features the users care about the most are not necessarily the features that get exercised the most internally. This has practical, noticeable consequences. Since RIM's development culture grew up on the concept of using dogfooding to ensure quality, they didn't develop a strong culture for other forms of quality control, such as automated testing. This has resulted in a gradual decline in overall device quality, something that a lot of people have been complaining about lately. The good news is that it's not hard to fix - they just have to stop relying as much on dogfooding and work on other more robust methods of quality control (which is something they're working on).

In general, I think this is a problem for most software projects that follow the Bazaar model of software development. The first guideline put forward by Raymond in his essay is that "every good work of software starts by scratching a developer's personal itch". I don't know if that's always true, but I think that as any such software grows, it will reach a point where it has features not really used by the developer. This also results in a "progressive divorce of the designer from ... the user", as Brooks puts it. Therefore projects that grow past this point have to face the same issues of miscommunication that Brooks talks about in this section.

In Chapter 16, Brooks mentions in passing that "complete modularity also has drawbacks ... optimized designs have components that achieve multiple goals." It occurred to me when reading this that there is a distinction between modular goals and modular components. A component that satisfies multiple goals is good, but a goal that is satisfied by multiple components is bad. He seems to define "complete modularity" as a one-to-one mapping between a goal and a component, whereas I would just leave it at components that don't interact with each other. I might just be a semantic definition issue, but it's something to think more about.

Anyway, that's all I have. It's a pretty thought-provoking book, and full of lots of good advice and insight, so if you're interested in designing stuff, I definitely recommend reading it.

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