A function is a unit of business activity that is less complete than a process.  Functions can be active (initiating, transforming, conveying) or passive (storing and receiving).

Figure 8

Functions are accomplished by some number of discrete actions.  They are invoked in various orders, to form processes (which means the same function may appear in many processes).  Functions are performed by individuals and/or organizations in roles.  They are triggered, and in turn initiate, flows of resources and control.  Functions are governed by rules, which dictate how flows should be initiated and directed.  Functions produce identifiable results, but these tend to be interim results that contribute to the ultimate results of processes.  At the function level we can see the transformation of resources into interim and final results.