A data dictionary is simply a repository for
information about the database- data definitions and characteristic such as
usage, physical representations, ownership, authorization, and security.
The DBMS can access the data dictionary to
determine the information it needs to operate. For example, the DBMS can access
the data dictionary to
- Determine if a data element already exists before
adding. This reduces data redundancy
- Change the description of a data field. For Example, to
change the description of a 20-position alphanumeric field to a 25-character
alphanumeric field, only the description in the data dictionary need to be
- Determine what relationship exist between the elements.
- Determine what applications programs can access what
The data dictionary is also useful to
programmers and system analysts.
- A programmer can copy a definition directly from the
data dictionary for use in an applications program. This guarantees greater
accuracy with less work from the programmer.
- If a data description is changed, the data dictionary
can be consulted to determine all affected applications programs.