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Now that we know what the requirements are and

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their main types, let's discuss where requirements come from and

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there are many possible sources for requirements so I'm

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going to list here the main ones. The first one are

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clearly stakeholders, anybody who is effected by the system

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and its functionality. Customers, users, and so on. The second

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typical social requirement is the application domain. For example,

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the fact that my software is running within a bank,

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or within a school. Why is the application domain a

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social requirement? Well, because there are constraints that are characteristics

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of the application domain that will affect the functionality of

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the system. For a simple example, just think about regulations.

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So banking regulations and school regulations in these cases. Those

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are things that might affect the functionality of my system

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and, therefore, that may become part of my requirements. And,

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finally, documentation can be an additional source of requirements. For example,

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notes, papers, manuals, books. So everything that refers to

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the functionality of the system that we're going to build.