Function

Function is all about the doing part - the business activities. When it gets down to it, function / process is all about taking information in, doing something to it and then passing it on. Sure, actual physical things happen, like a product is taken off a stock room shelf and sent in the post to the customer who placed the order. But you're not nearly as interested in what physically happens as you are interested in data about those things.

When you're thinking about or modelling function, these are the questions you'll be finding answers for.

What is being done (process)? By whom (users fulfilling roles)? Where? Where does information originally come from (external entities - people, other systems, other organisations)? What information is passed from activity to activity (data flows)? What data actually flows (entities and attributes)? Where is the info held when it comes to rest (datastores)? Where does information finally go (external entities)?

There are also non-functional aspects that you'll also be interested in:

Volumes: How many? How often? Are there peak times throughout the year / month / day?

Security & Access: Who is allowed to do what? Who is allowed access to what? What is done to protect data? For how long must data be archived? Are copies taken of important things and held off site? In the event of a failure, how long before things must be back to normal?

Business continuity / disaster recovery: Are there policies that dictate what is required of any business change in these respects? If not, is it in your scope to cover off as much of good practice as possible?

Legislative: How does the Data Protection Act apply? Does the business have to adhere to a code of practice? Do things like the Distance Selling Regulation apply?