Definition:
A data dictionary is a comprehensive description of each field in a database. It contains information about the characteristics of each item entered in the database, such as the field names, data types, field sizes and field descriptions.
Components of data dictionary:
- Field name
- Data type
- Field size
- Description
Data types:
Example:
More on Data Dictionary: [Ref: Oracle's website ]
-Is a read-only set of tables that provides information about the database. A data dictionary contains:
- The definitions of all schema objects in the database (tables, views, indexes, clusters, synonyms, sequences, procedures, functions, packages, triggers, and so on)
- How much space has been allocated for, and is currently used by, the schema objects
- Default values for columns
- Integrity constraint information
- The names of Oracle users
- Privileges and roles each user has been granted
- Auditing information, such as who has accessed or updated various schema objects
- Other general database information
The data dictionary is structured in tables and views, just like other database data. All the data dictionary tables and views for a given database are stored in that database's SYSTEM tablespace.
Not only is the data dictionary central to every Oracle database, it is an important tool for all users, from end users to application designers and database administrators. Use SQL statements to access the data dictionary. Because the data dictionary is read-only, you can issue only queries (SELECT statements) against it's tables and views.
SQL server table data dictionary:
Ref:
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