The base dictionary database defines the underlying structure for the data dictionary. An application database is initialised by making a copy of the empty base dictionary.
Each time you add a table or field specification to your database, the information is added to the base dictionary on your application database. Report Writer and QA Build programs are also stored in the base dictionary. Normally, there is no reason for you to know how your database is implemented, and so this information is hidden. However, you can access the underlying database by specifying a command tail to the DP4 utility programs.