Software has been proposed to solve a business problem in my company. After investigating the existing process, I discovered that for the proposed commercial off-the-shelf software to work -- some additional work would have to be done to it. What I'm confused about is what specification I should use to document the work needed -- a full software requirements specification (SRS) or a use case spec doc. With the use case spec I know it will be much easier for the vendor to know exactly where to tweak their software. Also, I know the use case spec will specify the functional requirements, but should the non-functional requirements go in the same use case req doc?

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