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Re: [XP] Alan Cooper vs Essential Requirements

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  • Dale Emery
    Hi Jeff, ... That s right. Lucky for me that s not what I m talking about. ... Right. You ll need to know what specific external events the system must
    Message 1 of 34 , Dec 4, 2002
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      Hi Jeff,

      > > McMenamin and Palmer (Essential Systems Analysis) claim that
      > > the *essence* of a system -- the technology-free expression
      > > of the system's responsibilities [...] -- is quite stable.
      > > [...]
      >
      > Yes, I'm sure the requirement "I want a system that will enable our
      > distributed sales force to track appointments, make sales, and see
      > up-to-date information on order fulfillment" will be quite stable.
      > But I can't implement that.

      That's right. Lucky for me that's not what I'm talking about.

      > To implement a system, I'll need *substantially* more detailed
      > information.

      Right. You'll need to know what specific external events the system
      must respond to, and how specifically the system is obligated to
      respond to each event. McMenamin and Palmer describe the system's
      response in terms of essential activities and essential memory. They
      define essential activity as any activity that "the system would have
      to do even if you could implement it with perfect technology" [more
      about that below]. Essential memory consists of "all the data that
      the system would have to remember if all it did was carry out the
      essential activities."

      MeMenamin and Palmer define perfect technology as having two basic
      components: perfect processors and perfect containers. A perfect
      processor "would be able to do anything and everything instantly; that
      is, it would have infinite capabilities and infinite workload
      capacity. It would cost nothing, consume no energy, take no space,
      generate no heat, never make a mistake, and never break down." A
      perfect container "wouldn't cost anything, and it would be able to
      hold an infinite amount of data. Any processor would be able to
      access conveniently the data it carried."

      To define the essence of a system -- what the system would do if
      implemented with perfect technology -- you gotta get into the details.
      But they are details about the system's obligations and not details
      about the technology in the system. III claims that the specific
      details that make up the essence of a system are far more stable than
      what people often offer as requirements. (I recently saw a "business
      requirements specification" that consisted of 250 pages of screen
      shots. That ain't essence.) I've never heard anyone claim that
      essence is fixed.

      Dale
    • Dale Emery
      Hi Jeff, ... That s right. Lucky for me that s not what I m talking about. ... Right. You ll need to know what specific external events the system must
      Message 34 of 34 , Dec 4, 2002
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        Hi Jeff,

        > > McMenamin and Palmer (Essential Systems Analysis) claim that
        > > the *essence* of a system -- the technology-free expression
        > > of the system's responsibilities [...] -- is quite stable.
        > > [...]
        >
        > Yes, I'm sure the requirement "I want a system that will enable our
        > distributed sales force to track appointments, make sales, and see
        > up-to-date information on order fulfillment" will be quite stable.
        > But I can't implement that.

        That's right. Lucky for me that's not what I'm talking about.

        > To implement a system, I'll need *substantially* more detailed
        > information.

        Right. You'll need to know what specific external events the system
        must respond to, and how specifically the system is obligated to
        respond to each event. McMenamin and Palmer describe the system's
        response in terms of essential activities and essential memory. They
        define essential activity as any activity that "the system would have
        to do even if you could implement it with perfect technology" [more
        about that below]. Essential memory consists of "all the data that
        the system would have to remember if all it did was carry out the
        essential activities."

        MeMenamin and Palmer define perfect technology as having two basic
        components: perfect processors and perfect containers. A perfect
        processor "would be able to do anything and everything instantly; that
        is, it would have infinite capabilities and infinite workload
        capacity. It would cost nothing, consume no energy, take no space,
        generate no heat, never make a mistake, and never break down." A
        perfect container "wouldn't cost anything, and it would be able to
        hold an infinite amount of data. Any processor would be able to
        access conveniently the data it carried."

        To define the essence of a system -- what the system would do if
        implemented with perfect technology -- you gotta get into the details.
        But they are details about the system's obligations and not details
        about the technology in the system. III claims that the specific
        details that make up the essence of a system are far more stable than
        what people often offer as requirements. (I recently saw a "business
        requirements specification" that consisted of 250 pages of screen
        shots. That ain't essence.) I've never heard anyone claim that
        essence is fixed.

        Dale
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