OK hows about this... Design is important cause software engineering is hard. Gifted engineers are able to code with little written design as soon as other engineers are added then design becomes very important. Or to put it another way if you have one programmer who is dead smart then he (or she) may be able to skip the design phase and still produce a damn fine project. As the project grows in size the requirement for design rises exponentially. XP programming simply stated avoids the issues because it quite rightly says that design is hard so we wont do it. You have correctly explained why design is hard, all of your points are valid.. However it is important to realise the cost fractionalising the design, the benifit is easy to see. Picking a point at random: software requirements change all the time so in a traditional environment we will have to change the design and the code that takes lots of time. In our XP world we have no design to update so we only have to update the code (although I have written this flippantly I do not mean it be so this is a genuine reason why XP is good) The problem is you have no design so each change becomes a little harder to implemnt as the impact is harder to see because there is no big picture, because there is no design.

Formal design is required for the following (off the top of my head) reasons

• To allow agreement between developers upon interfaces and functionality. A large project will have many elements all ready to collide the design will ensure that they all use the same messaging protocol and so on.
• To provide a road map for developers to be able to explore code they did not write or were not invloved within (or have simply forgotten). No matter how good a developer is he (or she) will get up to speed more rapidly with a design document that code. Reverse engineering is hard (trust me that is what I am doing now)
• To allow for impact analysis to take place regarding changes to core processing.
• To provide a common understanding of where you are trying to get to before you arrive.
• ... and so on and so on

I have looked at XP with interest but never tried it. My impressions are all negative please let me know how you get on with it.. I would love to be wrong and for XP to work.. twould certainly make our lives easier.
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Zigster

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