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Re: [XP] How much is too much?

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  • yahoogroups@jhrothjr.com
    From: Phlip To: extremeprogramming@yahoogroups.com
    Message 1 of 4 , Jan 30, 2005
      From: "Phlip" <phlip2005.at.gmail.com@...>
      To: "extremeprogramming@yahoogroups.com"
      <extremeprogramming.at.yahoogroups.com@...>
      Sent: Saturday, January 29, 2005 9:45 PM
      Subject: Re: [XP] How much is too much?


      >
      > Kent Beck wrote:
      >
      >> It sounds like you are feeling overwhelmed at having not enough time.
      >> XPE2
      >> contains a corollary practice called Incremental Deployment which
      >> suggests
      >> that the best way to replace a legacy system is to gradually take over
      >> its
      >> workload. Is there a little chunk of the legacy functionality you could
      >> replace in a week or a month? If you can, then you can turn that
      >> donkey/carrot thing around. By proving the value of your efforts, you're
      > the
      >> one holding the carrot.
      >
      > How are end users expected to enter names and addresses into the old
      > system,
      > launch the new system, enter shoe size, and enter the fictitious key
      > linking
      > to the old system?

      Martin Fowler sketches out the approach in:
      http://martinfowler.com/bliki/StranglerApplication.html

      There was a very nice article somewhere (unfortunately, I've lost
      the somewhere - apologies to the author) about how you incrementally
      do it. The article had a bunch of diagrams; great stuff.

      The article itself described a system (phone service requests)
      where the new system was to allow a customer to enter a
      service upgrade request over the web, while the old system
      continued to be used for updates by the telco's internal staff.

      The approach was to open up the old system so that the
      new system could use it as a back end, and likewise
      to design the new system so the old system could use it
      as a back end, each for the functions which that system
      would do.

      Once you've got the harness in place, cutting over functionality
      is easy, and you can deploy lots of stuff that doesn't affect
      the old system's UI as frequently as you wish - the effect
      is going to be invisible to the users. (The new system's
      UI can be updated at will - customer Web interfaces
      change UIs all the time.)

      John Roth

      >
      > --
      > Phlip
      > http://industrialxp.org/community/bin/view/Main/TestFirstUserInterfaces
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