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What is the Dictionary?...
Set of tables and views containing information about the database
- “Metadata”
- The information is stored inside the database
- The database contains information about itself!
Base tables owned by user SYS
- e.g. SYS.TAB$ table
- Too cumbersome to use regularly
Notes:
The Oracle Data Dictionary is a set of tables and views containing information about the database. This information is stored inside the database, so the database contains information about itself, often called “metadata.”
There are hundreds of data dictionary tables and views. The views are built on underlying base tables such as SYS.TAB$. However, the underlying tables such as SYS.TAB$ are difficult to use, in part because they are not documented and in part because the column names are not intuitive. (For fun, execute the SQL*Plus DESCRIBE command on SYS.TAB$. I think you will agree that the column names are not intuitive.)
Rather than use the SYS tables, we will use the more convenient – and documented – data dictionary views.