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Data Dictionary

   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

  1. Determine if a data element already exists before adding. This reduces data redundancy
  2. 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 modified.
  3. Determine what relationship exist between the elements.
  4. Determine what applications programs can access what data elements.

   The data dictionary is also useful to programmers and system analysts.

  1. 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.
  2. If a data description is changed, the data dictionary can be consulted to determine all affected applications programs.

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