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Interview of Dan North and Elizabeth Keogh

March 5th, 2009 No comments

The video of the interview is here.

First you get the UI, behind that there is code that gives benefit to the UI, and behind that there’s code that gives benefit to that piece of code, is smaller and more specific bits until the feature works.  The Domain Language is used all the way through.  Dan North tells a story…  While the developers were struggling with how to handle credit derivatives, a domain expert (a former trader) came by.  Because the developers were talking in the Domain language, the expert didn’t know they were even talking about code.  He thought they were talking about derivatives themselves and explained exactly how they work, giving them the algorithm.  

Scenario (and example) are words that the customer has a natural understanding for (unlike use case), that flesh out behaviors: given this situation, what to you want the software to do – what is the outcome?

  • Stakeholder: someone who has an interest in the work being done
  • Business analyst: expert in helping stakeholder articulate what they want in abstract terms e.g. “withdraw cash”
  • Tester: gets concrete with it e.g. “what does withdraw cash mean?  If I have $100 and withdraw $20, what is the result?”

This eliminates misunderstanding between the stakeholder and the developers as to what “done” actually means.

Using “should”  has two benefits.  Firstly, it forces you to focus on the class under test, because behaviors that don’t belong to that unit will not fit the “should” format.  Also, it allows the space to continually question “should it actually do this?”  This will have the documentation (the tests) naturally evolve with your understanding of the domain.

North describes different methodologies as:

  • Top-down – start with one big unit and keep breaking it up into smaller pieces
  • Bottom up – start with frameworks/architects and hope to solve the problem
  • Outside-in (BDD) – using the language of the domain, distinguish outer-most layer (e.g. scenarios) and work in from there.  The inner-most layer is the domain itself.  The UI is the third layer, which describes how the user interacts with the software.  In total, the question is “how do I describe software [interaction method] that [behavior in domain]?”  e.g. “how do I describe software [on the web] that [helps me plan the best shipping routes]?”

He concludes by suggesting that developers who are ingrained in the domain language can actually become part of the process of discovering business value, as they bring their level of understanding to the domain.

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