Tag Archives: computerscience

Extreme Programming Explained

Introduction

Naturally the key selling point of Extreme Programming — reduced risk and increased fun — appeal to me. I’ve worked on many projects that were either risky, no fun or both and any way to improve that would be a good idea.

However, most of the successful projects were run using fairly heavy-weight methodologies, CMM or ISO accredited, for example. Extreme Programming promises to deliver the benefits while still being simple. I was sceptical. This sounds a little too close to one of Fred Brookes Silver Bullets.

How does it work?

Extreme Programming sounds too simple to ever work. None of its components are new or especially controversial, some are even very common throughout the industry. What’s new is their application together. The key is that the strengths of one part paper over the weaknesses of others.

I won’t detail all the bits — that’s what the book is for — but there are a couple of things I want to talk about.

The one thing that came through in all other reviews of the book was the pair programming aspect. The idea is that whenever writing code, there are always two people sat at the computer. This sounds very wasteful of resources but is based on some very sound theories: reviewing code is good and sharing knowledge around the team reduces the dependency on any one person. XP takes it to the extreme (hence the name) by having, in effect, every line of code being reviewed by two people all the time.

I can certainly see the benefits, but I can imagine a client being very suspicious when you suddenly have two people appearing to do a job you previously only had one doing. He also proposes using a utilisation metric which documents that people are actually not doing genuinely productive work all the time.

Anyone that writes software will immediately recognise that a lot of time is spent helping colleagues, in design or review meetings and any number of other things that are not directly and visibly related to increasing the functionality of a program. Making it more visible sounds like a much harder “sell” than is suggested in the book.

Is it easy to understand?

Brock is clearly very enthusiastic about his methodology and this shows in his prose, which is clear, friendly and concise. It’s sensibly organised and it usually answers questions you’re thinking of in just the right place.

However, it only does all that if you remember what the book is trying to explain. It’s trying to explain Extreme Programming not how to implement it effectively. I had a little difficulty seeing how you could automate tests in some environments. We tried and failed with Oracle Forms (or whatever it’s called this week) for example. I don’t disagree with the principle, but there are some definite technical barriers that are not even acknowledged.

I’m not sure that the distinction between describing what XP is and how to implement it is a good one. It sounds like an excuse to sell two books when only one would suffice. Why would anyone be interested in learning the theory but not the practice of a simple methodology?

Disadvantages

Beck does not claim that Extreme Programming works in all circumstances. There’s an entire (albeit short) chapter on it, which is quite refreshing. Most people would claim that their baby was ideal in all circumstances!

I only thought of a couple of other problems that are not addressed, although neither are necessarily any more of a problem with XP than with other methodologies. (However, they are areas that are claimed to be addressed.)

Documentation is never kept up to date anyway, and in XP there is a much greater chance of at least one person knowing how it works. Couple that with a full set of tests, the ‘business’ person being on the team right from the start and, well, what’s my problem?

The problem is identified in Death March. Who are the stake holders on the project? Is it your team-member (the end user)? Is it their manager, who might want a bunch of reports? Is it the CTO who doesn’t actually care what the system does and just wants a success of some kind in order to get promoted?! The book and the Extreme Programming approach treat the problem of requirements as something that is eventually known and is fix-able given close enough interaction with the users. I wish that were true.

Beck might suggest that this ‘unknown’ is just another form of change than can be managed in the normal manner, but my guess would be that the magnitude of changes required by people that don’t have day-to-today access to the team would be too big and would break the process.)

Or perhaps this is just a size issue. With a system, with a small number of well-defined users there’s no reason it couldn’t work.

Conclusion

I think my initial and immediate dislike of XP stemmed from the fact that most of the projects I’ve ever worked on have fallen into the “won’t work” camp. Now that I understand its background I can appreciate it much more.

And it’s only fair to note that this appreciation comes solely from the book. It’s worth reading even if you don’t plan on implementing Extreme Programming.

The facts

Author: Kent Beck

Cost: $29.95

ISBN: 0-201-61641-6