An ideal data dictionary should have everything a DBA wants to know about the database.
1 Conceptual, External, and internal database descriptions.
2. Descriptions of attributes (fields), entities (record types) as well as origin, cross- references and meaning of data elements.
3. Authorisation ,Synonyms and security codes.
4. Which external schemas are used by which programs, what their authorisations are, and who the users are.
5. Statistics about database and its usage containing number of records, etc.
A data dictionary is executed as a database so that users can query its contents. The cost efficiency of a data dictionary increases as the difficulty of an information system increases. A data dictionary can be an enormous asset not only to the DBA for database design, execution and maintenance, but also to managers or end users in their project planning.