What does Data dictionary Mean?

A data thesaurus is a document or a set of records that has a database's metadata. The data dictionary consists of records around other objects in the database, such together data ownership, data relationship to other objects, and other data.The data dictionary is a critical component of any relational database. That provides additional information around relationships between different database tables, help to to organize data in a neat and easily search way, and prevents data redundancy issues.

Ironically, because of that is importance, it is invisible to most database users. Typically, just database administrators communicate with the data dictionary.

A data dictionary is also called a metadata repository.

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sdrta.net explains Data Dictionary

A Data Dictionary consists of information about attributes or areas of a details data set. In a relational database, the metadata in the data dictionary includes the following:

Names of all tables in the database and also their owners.

Names of all indexes and also the columns come which the tables in those indexes relate.

Constraints defined on tables, consisting of primary keys, foreign-key relationships to other tables, and also not-null constraints.

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Additional physical information about the tables including their warehouse location, warehouse method, etc.

For example, a advertising bank's database include information about clients can have attributes for client name, birth date, street address, jae won savings, account and also credit card number, loans, etc.

Each attribute occupies a heat in a spreadsheet, while assorted columns provide extr elements that describe that attribute (whether it’s optional or forced for a record, the form of data, that is location, etc.).

A data dictionary might look prefer the one below:

*

For most relational database administration systems (RDBMS), the database monitoring system software requirements the data thesaurus to accessibility the data within a database. Because that example, the Oracle DB software needs to read and write come an Oracle DB. However, it have the right to only perform this via the data dictionary created for that certain database.For instance, following the above bank's database example, the administrator wants to recognize which table stop information about loans. Making an education guess the the table many likely has the indigenous "LOAN" in it, the would problem the adhering to query top top the data dictionary (the first query is for an Oracle DB, if the second is because that an SQL Server DB):

SELECT * indigenous DBA_TABLES wherein TABLE_NAME prefer '%LOAN%';

SELECT * native SYSOBJECTS whereby TYPE='U' and also NAME like '%LOAN%';

A data dictionary can be either energetic or passive. The may occur that the structure of the database has to be changed, such regarding add new attributes or to eliminate some obsolete ones. If those alters are updated instantly in the data dictionary by the database monitoring dictionary, then the data dictionary is an active one.

Conversely, if the database manager maintains the data thesaurus as a different entity that needs to be to update manually, the is described as a passive data dictionary. Various other than requiring added work to it is in synced, passive data dictionaries are prone to errors when data in the database and also dictionary execute not complement anymore.