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Iterative vs Incremental (was Re: [XP] Skeptical outsider & a dilemma (longish))

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  • Kay Johansen
    Alistair has a good definition. I liked Tom s also. I don t think they are the same. And now I am far from sure what the heck I meant when I used the term
    Message 1 of 1 , Jan 17, 2001
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      Alistair has a good definition. I liked Tom's also. I don't think they are the same.
      And now I am far from sure what the heck I meant when I used the term incremental in my
      recent posts. :-o

      Tom Mostyn wrote:
      [I]ncremental devleopment is where you release your
      product in increments. Each successive release contains more
      functionality coming closer to what the customer wants as a whole
      product. Iterative development is where you have multiple cycles of
      analysis, design, code and test within an increment.

      Alistair wrote in Surviving OO Projects, p. 10:
      "Incremental development involves completing parts of the system at different times and
      at different rates; it does not imply revising any part of the system already
      completed. The aim is to improve the quality of the process by fixing errors in
      knowledge about the software development process.
      "Iterative development involves reworking a part of the system to improve the quality
      of the system. The user interface and the infrastructure of a system are two parts of
      software systems that benefit the most from the improvement. The user interface is
      improved to better serve the users, and the infrastructure is improved to simplify the
      evolution of the system."

      I wonder why Alistair doesn't mention the reason I think of for doing incremental
      development. My reason has little to do with improving the software development
      process. I would want to do it to reduce risk -- would you rather have three completed
      features by March 1, or six partially completed features?

      But I am probably still misinterpreting "incremental" as Alistair defines it. On p. 118
      of Surviving OO projects, he continues:
      "Incremental development is a staging strategy in which portions of the system are
      developed at different times or rates, and integrated as they are completed. It does
      not imply, require, or preclude iterative development or waterfall development, which
      are rework strategies. The alternative to incremental development is to develop the
      entire system as one lump deliverable."

      He goes on to explain how incremental development can give staff an "aha!" feeling of
      comfort by going through the entire process (whatever your process is) in a reasonably
      short time. "It lets them start the next round of development with an understanding of
      what is going to come and how the early activities affect the later activities."


      Jim McFarland wrote:

      > ----- Original Message -----
      > From: "Phlip" <pplumlee@...>
      > > Oh, my goodness. You've attributed to me a distinction I'm incapable of
      > > making. I would have said either without thinking.
      > >
      > > If there's a difference in methodological research between Iterative and
      > > Incremental I never heard of it. If forced to guess I'd say Iterative was
      > > like XP or Prototyping, and Incremental was like Spiral (the kind where
      > the
      > > developers prioritize the feature list, and each trip around the wheel
      > gets
      > > bigger & slower).
      > Who said anything about methodological research or comparing XP to other
      > approaches? We were just distinguishing between two different qualities
      > that a process may have. Tom Mostyn's post gives good definitions of the
      > terms. Also, see page 10 in Alistair Cockburn's "Surviving Object-Oriented
      > Projects" for a good comparison/definition of iterative and incremental.
      > For the record, XP is both iterative and incremental.
      > later...
      > jim
      > To Post a message, send it to: extremeprogramming@...
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