School of Information Systems

What is Data Dictionary Object in Oracle?

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. 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 tablespace.

The data dictionary has three primary uses:

  • Oracle accesses the data dictionary to find information about users, schema objects, and storage structures.
  • Oracle modifies the data dictionary every time that a data definition language (DDL) statement is issued.
  • Any Oracle user can use the data dictionary as a read-only reference for information about the database.

A data dictionary contains metadata i.e data about the database. Example of metadata:

Relational databases (most common type of database) store and provide access not only data but also metadata in a structure called data dictionary or system catalog. It holds information about:

  • tables,
  • columns,
  • data types,
  • constraints
  • table relationships

The users of the database normally don’t interact with the data dictionary, it is only handled by the database administrators.


Nur Anisa