Joel On Xp (Again)

Recently Joel wrote: http://www.joelonsoftware.com/articles/AardvarkSpec.html

In this article Joel talks about the 20-page functional spec he wrote for his Aardvark project. He notes that by thinking through the spec he was able to avoid a number of problems that could have delayed his project. From this he concludes:


Oh Joel! First of all a 20 page function spec (with a big coding standards section in the middle) is not a BIG DESIGN UP FRONT. A BDUF is 1000 pages of UML diagrams that plan out every intimate little detail of how the system will be built, before any code is written. If you doubt that companies write such silly tomes, let me correct you. Some companies glory in making sure that absolutely every class is described in a class diagram, and every method is described in interaction diagrams. Some development teams describe the entire static structure and the entire execution flow of their projects, before writing a line of code. THAT is BDUF, Joel. And it's completely insane.

No, Joel, your little functional spec was just a little functional spec. It was a good document, and you were right to write it. I would not be surprised if an XP team wrote a document like this; nor would I yell at them for blasphemous behavior. Writing a little spec like this is perfectly appropriate.

If you read the XP/Agile literature carefully you will find that XP demands that a document like this be written. Yes, it's true that XP wants the document written incrementally. It's true that XP does not want the whole document written in detail up front. On the other hand XP does want each iteration's worth of the spec written in hideous detail, in the form of automated acceptance tests. What's more, XP does want a rough outline of the document (i.e. the release plan) written before the iterations begin.

Oh there are some differences for sure. An XP team would be more likely to write the release plan on a set of index cards. They would be more likely to formalize the requirements at the beginning of each iteration by writing FitNesse tests (See www.fitnesse.org). They would be more likely to work out a lot of the functional behavior in CRC sessions or conversation, before writing the acceptance tests. On the other hand an XP customer (like you might be) might very well write a document in exactly the form you chose, if there was a need (like communicating with a bunch of summer interns that you couldn't sit down and work with). XP doesn't tell you not to write a document like this. XP simply tells you to convert it from a outline to a formal document in increments, which are usually one or two weeks long.

Joel, You write a lot of good stuff. It would be even better if, before you bashed XP any more, you actually took the time to understand what XP is. You might find that the XP community is comprised not of a bunch of wild-eyed "fanatics", but of a group of sincere old-timers who simply want to teach the industry (these kids nowadays!) how to take small, careful steps.

Uncle Bob.

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