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In our initial definition of requirements engineering, we talked about

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software systems. But what do we really mean when we

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use the term software? Software is an abstract description of

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a set of computations that becomes concrete, and therefore useful, only

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when we run the software on some hardware, and that,

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in the context of some human activity that it can

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support. So what does that mean exactly? What that means

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is that when we say software, what we really mean is

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a software intensive system. That is, the combination

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of 3 things, the software, the hardware on which

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the software runs, and the context in which the

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software is used. Just to illustrate, let me show

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you this through a picture. What I'm showing here

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is a customer, a user, that is using, is

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accessing, an ATM machine. And this action involves several

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things. There is the software that drives the logic

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of the ATM machine. There is the hardware on

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which the software runs. And there is the context

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In which the software is used. And in this

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case, the context is the bank. And only by

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considering these 3 things together can we really understand

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the functionality that is represented here. So the bottom

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line here is that we usually take hardware and

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context for granted in this equation. But they actually

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need to be explicitly considered when building a

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system. Otherwise, we might forget this is all

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the functionality, and ultimately of the requirements. And

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we might end up with the wrong system.