Python Rocks! and other rants

Weblog of Kent S Johnson

2004-05-03 08:56:32

Design and coding

I have thought of an interesting way of describing the relationship between design and coding in different development styles.

A (sadly) popular style of development is code-and-fix programming. In this style, the goal is to do the minimum required to get something that appears to work. At its worst this is coding without design, at any rate without thinking seriously about design or architecture or long-term viability. It leads to unreadable, unmaintainable code, cascading defects and many other problems.

Big Design Up Front (BDUF) is a response to this style. BDUF attempts to figure out the solution in the abstract before starting to implement it. This is design without coding. This approach has many problems as well. It is hard to figure out a good design without the hands-on knowledge you get from writing code. It is brittle and unresponsive to changing requirements. It takes considerable effort to create and maintain design documents.

The agile approach is a middle way. It disdains both sloppy hacking and excessive design. Agile programmers think about what might work and try it. They refactor when they have a better idea or when the requirements change. They keep growing the design.

Agile development is sometimes feared because without up-front design it must be "just hacking". If you aren't designing up front, with formal process and documents, you must not be designing at all. This fear is born from the reaction to code-and-fix programming and thinking that code-and-fix is the only alternative to BDUF. This is a false dichotomy and a false perception of agile development.

Design and coding work best when taken together. If you try to think your way through the design without writing code you lack the on-the-ground knowledge you get from coding. If you just start writing code with the sole goal of getting something that seems to work, you are hacking in the worst sense of the word. But if you consider each addition to the code carefully and keep the code clean at all times you will end up with a thing of beauty - well-designed code that is superbly suited to the task at hand.

Note: Ned Batchelder's blog about the similarity between diamond cutting and the decisions that must be made while designing a software system was the spark that led me to this idea.