Not sure whether you checked the below PDN article for getting the OOTB DB details. If you still need more details, may be you have to dig into Pega Help or PDN. I don't think we have a document provided with all DB specs. It is your wish to keep it in a doc or read them online.
We do not normally document the OOTB db tables (not yet at least), but you can get the DDL during installation (or simply run generateDDL.bat/sh to get the all the OOTB DDLs). Keep in mind that DDLs are different from version to version potentially.