Dr. Codd actually defined 13 rules 0-12 but they are referred to as Codd's 12 Rules for the relational model.
0. Foundation Rule-- A relational DBMS must be able to manage databases entirely through its relational capabilities.
1. Information rule-- All information in a relational database (including table and column names) is represented explicitly as values in tables.
2. Guaranteed access-- Every value in a relational database is guaranteed to be accessible by using a combination of the table name, primary key value, and column name.
3. Systematic null value support-- The DBMS provides systematic support for the treatment of null values (unknown or inapplicable data), distinct from default values, and independent of any domain.
4. Active, online relational catalog-- The description of the database and its contents is represented at the logical level as tables and can therefore be queried using the database language.
5. Comprehensive data sublanguage-- At least one supported language must have a well-defined syntax and be comprehensive. It must support data definition, manipulation, integrity rules, authorization, and transactions.
6. View updating rule-- All views that are theoretically updatable can be updated through the system.
7. Set-level insertion, update, and deletion-- The DBMS supports not only set-level retrievals but also set-level inserts, updates, and deletes.
8. Physical data independence-- Application programs and ad hoc programs are logically unaffected when physical access methods or storage structures are altered.
9. Logical data independence-- Application programs and ad hoc programs are logically unaffected, to the extent possible, when changes are made to the table structures.
10. Integrity independence-- The database language must be capable of defining integrity rules. They must be stored in the online catalog, and they cannot be bypassed.
11. Distribution independence-- Application programs and ad hoc requests are logically unaffected when data is first distributed or when it is redistributed.
12. Nonsubversion-- It must not be possible to bypass the integrity rules defined through the database language by using lower-level languages.
