Nothing fancy... this matches our dimension setup in Dynamics AX. Forecaster uses Microsoft SQL Server (no surprise there) to store data and if you have SQL Server Manager installed, you can peek at the raw tables. I am using SQL Server 2008R2 Management Studio.
Once you find the right database engine and database, you should see lots of entries under Tables. In our configuration with two segments, Department data can be found in table dbo.M_SEG0, and Account data can be found in table dbo.M_SEG1 (screen cap below):
These specific tables only store segment information. The actual financial data is stored in table dbo.Z_RAW, which has segments and periods as fields.
Since I maintain the segment data manually, I can link directly (or use a pass-through query) to Dynamics AX dimensions to see if there are missing departments and accounts in Forecaster.