Recommendations on documentation of data model?

[Magnus Runesson]

I have started designing a data model/schema for a new application that 
will use Accumulo as data storage. I am looking for a good way to 
document my model in a way that makes it understandable for other 
developers that will use the same data in the future.

Does anybody here have good experience how to do it?
My first thought was using a spreadsheet just listing and describe the 
combinations of Family, Qualifier and requirements on the values.

Regards,
/Magnus