Answer by Andrew Mobbs ·
The data dictionary is where the Oracle RDBMS stores the logical and physical structure of the database; e.g. the objects in the database, the structure of your tables, where the datafiles are, which extents are used by which segments, what constraints exist, and so on.
It's usually queried through the static data dictionary views (DBA_<whatever> and so on) when you need to find out about the logical or physical structure, or the objects in the database.
Answer by Lars ·
Oh my gosh. The data dictionary is in my opinion very good to have. Searching for columns, searching for links, displaying information on the various objects you have in the database.
I often use SELECT * from DICT WHERE COMMENTS LIKE '%privilegies%' or something else I want to know more about tables or views in the dictionary.
THere are many goodies there.