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Another important distinction, when talking about requirements, is that
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between user and system requirements. So, let's start with defining
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user requirements. Those are requirements that are written for the
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customers and they're often in natural language and they don't
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contain technical details. And the reason for that is
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that their purpose is to allow customers, stakeholders, to check
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that the system will do what they intended. So it's
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a way for the analyst, the developers, to communicate with
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the customers, with the stakeholders. System requirements, on the
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other hand, are written for developers. Contain detailed functional and
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non functional requirements. Which we just discussed, and which
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are clearly and more rigourously specified than the user requirements.
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And the reason for this difference is that the
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purpose of the system requirements is to tell developers what
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to build. They must contain enough details so the
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developers can take them and use them to design and
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then develop a system. Just to give you a concrete
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example, here I'm showing you a user requirement that just says
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that the software must provide a means of representing and accessing
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external files created by other tools, and the corresponding system requirement.
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And as you can see, even if we don't read the
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whole requirements. The former is an informal and high level description
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of a piece of functionality, whereas the latter describes the same
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functionality but in a much more extensive and rigorous way. As
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I said, this is something that the developers can use to
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design and then build a system whereas this is something that
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can be used to communicate. With the stakeholders, with a non-technical
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audience. And we need to define both because they serve different purposes.
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