Codd's Twelve Rules - Rule 4 - Dynamic Online Catalog Based on the Relational Model
Rule 4 | Dynamic Online Catalog Based on the Relational Model |
Rule | The database description is represented at the logical level in the same way as ordinary data, so authorized users can apply the same relational language to its interrogation as they apply to regular data. |
Description | This rule requires that a relational database be self-describing. In other words, the database must contain certain system tables whose columns describe the structure of the database itself, or alternatively, the database description is contained in user-accessible tables. In other words, this rule insists a data dictionary that stores meta data. |
Example |
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Some DBMS that fulfills this property | SQL Server, MySQL, and Oracle. |
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