NDC 2010: Eric Evans – Folding together DDD into Agile

One of the most puzzling emails Eric have received was one claiming that his book really proved that up front design was important. In large this is a miss conception on how modeling happens. A tremendous amount of knowledge comes from actually implementing the software. You have the most insight at the end of the project. You have the most ignorance in the beginning of the project.

On the other hand Agilistas often declare that modeling isn’t necessary at all which is a miss conception of the importance of modeling. In short, the importance is tied into what your goal is and what you think is important.

Different goals, different requirements on modeling

  • If your goal is to just complete the next story, modeling isn’t that important. The span of your focus is just that story and a model doesn’t make sense. A lot of agile has this focus in Eric’s opinion.
  • If your goal is to complete a releasable set of stories with an acceptable level of bugs, some modeling will be required. Each story will have it’s own impact on the code and for them to behave well together, there has to be some design and thought.
  • If your goal is to deliver a release that the team can continue to extend in the next release, you will need a reasonable amount of modeling and design. First release won’t see a huge difference, but the second release will come out faster.
  • If your goal is to deliver a clear and cohesive user experience you’ll need a clear underlying model or it will be really hard to put a well designed user interface on top of it.

Modeling and TDD

With a green bar, TDD will give you A answer. It’s a correct answer, but the question is, is it the best model that delivers the answer? It turns out that finding the right answer is not quite good enough. We need to find the right answer that makes sense to a business person.

DDD and The Agile Process
Eric introduced a modeling sub process that he calls “Whirlpool” which helps in defining when and where modeling happens:

exploratory_cycle It’s currently a draft and you can read more about it @ http://domainlanguage.com/processdraft/

It’s really interesting to see how Eric tackles the ideas that modeling should be done upfront and the agile notion of very little modeling, and doing so with a piece or explained process. I don’t fully grasp what all parts of the process does or fit together, but I for one will follow the progress and try to apply it in my next scrum / kanban project I get into.

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  1. Pingback: Agile & Modeling new way of life! « Vincent Hanniet * IT Modernization

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