Data Dictionary

Data dictionary is used to store data item type and record types with other information. The information that is used it depends on the system which is being used. Data dictionary or data directories are used in creating and processing of the database and also it can store the database schema. In the early stage of design for collecting the information about the data then in this situation data dictionary play a vital role. The database administrator is responsible for controlling the access of data dictionary but the user should not aware. Actually dictionary contains a metadata. Data about the data in the database is called a metadata.

There are two types of data dictionary. 

If database management system has a data dictionary as a part then this type of data dictionary is called integrated data dictionary.

If data dictionary is not a part of particular database management system so we refer to it as a freestanding data dictionary. The difference between integrated and freestanding data dictionary is that integrated data dictionary is most important not only in design phase but also perform many function throughout the working of the database on the other hand freestanding data dictionary is used in initial design stage. Integrated data dictionary can be active or passive. In active integrated data dictionary, when database is processed then database management system check it every time. Active data dictionary is maintained automatically by the system because active dictionary is attached with actual database structure. But passive dictionary is not checked every time when database is processed. Why data dictionary is used??? What is the purpose of data dictionary??? What functions data dictionary offered??? 

The data dictionary performs a many function. Data dictionary provide a control over data as a resource because in data dictionary data is store in a central location. 

An exact definition of each item must be developed for the storage in the data dictionary. Data dictionary help to communicate with users. 

Data dictionary knows the interest of each person on the item. 

Redundancy and inconsistency in data item name is checked. Synonyms are accepted in the database. What is synonym???? Different names for the same items is called synonyms. Homonyms are never accepted in the databases. What is homonyms??? Identical names for different data item is called homonyms.

The changing (the addition of new data item and alterations in data item description) in the databases structure are identified. These changes are recorded in the data dictionary. 

The data dictionary is responsible for determining the impact of changes in the database structure. The database administrator notices the effects of these changes. The external, logical and physical models are recorded and mapping between models are also recorded. Data dictionary store the information about the identities who access the each item. The person who is responsible for updating each item must be listed in data dictionary.