I have been asked by senior management to create a document that
captures:
1. the business requirements that are realized by the current
system
2. the history of the system as it is impacted by new requirements

The company I work for is small and I am the only (newly-hired)
business systems analyst. For the most part, I have freedom to choose
what documents/models are "just good enough". I have created a core
set of documents that follow many of the guidelines set in "Agile
Documentation" by Andreas Rueping. I also try to adhere to as many of
the best practices for documentation as described on Ambysoft.com.

This request is tricky for me as I see the total cost of document
ownership quite high and the audience quite small, but I do see the
value in having a doc that offers "one stop shopping" for a high level
view of what the system does today and how it got that way.

I appreciate any ideas or points to consider.