Voicemail Question - FreePBX / Asterisk Database Structure

Hello Everyone,
I am trying to locate the field / table / database where voice mail flags are read and set. I would like to be able to read the field where the voicemail “Retrieved” flag is set. I am not very strong in databases but my co-worker is so I am helping to determine where this would be. Can anyone shed some light?
Ideally I would love to find any documentation with the full database schema.

I appreciate any feedback.