The data dictionary (or data repository) or system catalog is an important part of the DBMS. It contains data about data (or metadata). It means that it contains the actual database descriptions used by the DBMS. In most DBMSs, the data dictionary is active and integrated. It means that the DBMS checks the data dictionary every time the database is accessed. The data dictionary contains the following information.
• Logical structure of database
• Schemas, mappings and constraints
• Description about application programs.
• Descriptions of record types, data item types, and data aggregates in the database.
• Description about physical database design, such as storage structures, access paths etc.
• Descriptions about users of DBMS and their access rights.
A data dictionary may be a separate part of DBMS (non-integrated data dictionary). It may be a commercial product or a simple file developed and maintained by a designer. This type of data dictionary is referred to as freestanding data dictionary. This type of data dictionary is useful in the initial stage of design for collecting and organizing information about data. For example, each data item, its source, its name, its uses, its meaning, its relationship to other items etc. is stored in data dictionary.
• Logical structure of database
• Schemas, mappings and constraints
• Description about application programs.
• Descriptions of record types, data item types, and data aggregates in the database.
• Description about physical database design, such as storage structures, access paths etc.
• Descriptions about users of DBMS and their access rights.
A data dictionary may be a separate part of DBMS (non-integrated data dictionary). It may be a commercial product or a simple file developed and maintained by a designer. This type of data dictionary is referred to as freestanding data dictionary. This type of data dictionary is useful in the initial stage of design for collecting and organizing information about data. For example, each data item, its source, its name, its uses, its meaning, its relationship to other items etc. is stored in data dictionary.
