SQL Codd Rules

Dr E.F.CODD’s listed 12 rules for relational databases in 1985.

1. The Relational data base management rule

• A relational data base management system must use only its relational capabilities to manage the information stored in the database.

2. The Information rule

• All information in relational database must be represented as values within columns in rows.
• Pointers are variables that contain address of the memory location where the data is stored.

3. The Guaranteed Access rule

• Every item of data must be logically addressable with the help of a table name, primary key value and column name.

4. The Systematic Treatment of NULL value rule

• A relational database must support the NULL value for representing missing or inapplicable data.

5. The Dynamic On-line catalog Based on the Relational Model Rule

• The structure of the data base should be represented at logical level in a tabular form.
• The representation of database structure as a collection of tables is known as catalog or data dictionary.

6. The Comprehensive Data sublanguage rule

• An RDBMS support at least one clearly defined language that can be used interactively as well as can be embedded in programs (SQL).

7. The view updating rule

• All theoretically updatable views must be updatable in table.

8. The High-Level Insert Update and Delete rule

• The date retrieval from a relational database must be possible in sets that may comprise data from multiple rows or multiple tables.

9. The physical Data Independent rule

• The database user need not known about the physical implementation of data storage and retrieval.

10. The Logical Data Independent rule

• The data base user’s view of a data should not be effected by any change in the database tables (Materialized view).

11. The Integrity Independence rule

• Data integrity rule must be defendable in the relational database and should be stored in data dictionary.

12. The Distribution Independence rule

• The system must be able to access or manipulate the data that is distributed in other systems.

13. Non-subversion Rule

• If a database management system has a low level language, then it cannot be used to violate the integrity rules or constraints that have been expressed using a

higher-level language.

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