The answer – as many as you need!
Staff at iData, the company that provides Data Cookbook, recently published an analysis of the number of Functional Areas that each customer maintains. There are currently about 120 customers.
The median count of functional areas is 8, and the average is 11. The distribution is far from normal – one standard deviation (~9) in either direction covers nearly 90% of clients in the sample. The inter-quartile range runs from 6 to 13.
But almost 20% have more than 15, and at least half a dozen clients have more than 30 functional areas in their Cookbook instance.
For the record, at Rochester we maintain 12 Areas. When we started with Data Cookbook in 2013, we quickly set up about 7 Areas. In our first 6 months we added the remainder and have stayed steady at 12 every since. In the context of the iData analysis, we are about average.
The key thing to keep in mind is that a Steward (responsible for the definitions in their area of data expertise) is associated with every Functional Area, and the Steward comes first. If a new Steward comes forward, with expertise in an area of data not represented, a Functional Area would be created for him or her.