I think there’s a very good question here about how do you get stakeholders / users to validate requirements (in the general sense not just “the System should” type statements), but I that the concept of sign-off is flawed. What does it mean if the requirements have beed signed-off? It doesn’t mean that the requirements are correct, complete or that they won’t change, so why would you ask the users to sign-them-off, what good does it do?
In answer to your question, probably the worst thing you can do is to send them some sort of document and say “if I haven’t heard back by next friday I’ll consider them signed- off”
Interaction in the form of walkthroughs and workshops work well and are of relatively low cost, prototypes and mock-ups are better (especially if it’s high risk) but more expensive and then as Rudd says iterative and incremental development is best if you can do it.
1. Input parameters addition – what are the present parameters, how they contribute to arrive at the final figures, what are other conditions or constraints , business rules – like discounts, penalties due to missing TATs etc. which are likely to impact the normal billing figures etc. Actual Algorithm involving all these can be modelled into Excel. Different datacuts from your existing Database should be provided as inputs and see the outputs. It should be able to point out how new parameter is contributing – what was output with/without it. Data combinations builds confidence to a great deal.
2.In case of Billing output with additional points from other systems -e.g. CRM for missing TAT etc – Then we have to build a model which will introduce the integration points, How they will flow across systems – frequency modes, transformation rules etc. Their contribution towards assessing health of client-vendor relationships over the years.This can be provided through context diagrams/flow diagrams/business rules/Graphs etc.
3.Updated Logic – Algorithms/Logic – actual calculation steps to define every step in the processing – privilledges etc. should be modelled though Excel, With new logic in place what effect it will carry upon retrospective data should be mentioned into that – with effect date wise. Different artifacts should be employed to provide the clarity upon different dimentions of the process.
Continuous walkthroughs with end users, weekly update to owner/sponser helps to be on one page for the entire team. It avoids shockers and facilitate sign offs process.
Agile approach should be great many a times as it builds confidence between user communities fast than offline approach. But cases when ‘whether this investment is utmost necessary within this quarter itself’ is rather a question on business owner‘s plate then offline mode works great to get all the pieces aligned first. It is always important to select the correct approach and build a consensus fast and get the sign offs.