Pretty good question Surreyfrog. I had to think about it for a while. 

The way I view it is that a function - described by a use case - is something an actor would tend to do at one time. Say "book a ticket" in your cinema analogy. A process is something that has a number of activities / functions that tend to occur over a period of time. Something like process "See Movie at Cinema" which has activities like "View Whats On", "Book Ticket", "Drive to Cinema", "Park Car", "Collect Ticket", "Check Ticket", "Watch Movie", etc, etc.

Notice that some functions are manual and some are supported by a system. I recommend when you are modelling a business process to capture all functions in the process, including the manual functions.

Also notice that even this simple example has possible alternatives to include in the process like what if the Ticket is mailed or its an eTicket and you print it off before going. What if you pay when booking or pay when pick up the ticket. What if you walk to the cinema, etc, etc.

When you're modelling a process, what you thought initially was a simple function, when you look at it more closely, can turn out to be a process in its own right i.e. you may end up having nested processes.

Kimbo

 Hi Surreyfrog,

a process is as you defined it. A function is a reusable component in a process that has inputs and outputs that mean it can be used in many processes: it can be 'slotted in' to a process because in every process at that point it gets the same inputs and produces outputs needed by subsequent process steps. I think the concept comes from programming...an example might be "verify a customer" which you use as part of "place order" process and "issue refund" process.

Hard and fast rule? Hardly. Does it matter though? As a BA you need to model business processes - functions are not required to develop a full statement of business process requirements, process models and process steps are. If functions help, use them. If not, don't!

Hope that helps,

Guy