This question already has an answer here:
I inherited a project that I've been maintaining for approximately a year now. The project primarily revolves around performing various financial calculations for the end user. It's roughly 100,000 lines of spaghetti code held together with duct tape and gumption. I've been slowly going through and refactoring the code as I have to make changes to it, and adding inline comments where helpful, but there's no formal documentation.
I've been tasks with rewriting the software on our company's new platform (I know, the worst decision a person can ever make is a complete rewrite, but in this case it's necessary, as the entire architecture and framework involved is changing). As the first step of this, I need to come up with a set of functional requirements. However, I'm at something of a loss on where to start and how to go about it. The scope of it is just so enormous that I'm not even sure where to begin.
Has anyone else had a similar experience? Where did you start with the documentation for the new project? Are there any resources out there I could consult? I could write the technical specifications of it today without an issue, but I've never before had to write functional requirements.
I know it's not normally part of the developer's responsibility to write functional requirements - someone in the business department should do this. However, it was apparently decided I was the best person for the job as to most of the people in our business department, the way it works is just "magic".