Dr. E. F. Codd defined the 13 rules for a Relational Database Model. These 13 rules are referred as Codd 12 rules for the relational model.
Codd 12 Rules
Rule 0 – Foundation Rule
A relational DBMS must be able to manage databases entirely through its relational capabilities.
Rule 1 – Information Rule
All information in a relational database including table and column is represented as a value in a tabular format.
Rule 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.
Rule 3 – Systematic Null Value support
The DBMS provides systematic support for the treatment of null values.
Rule 4 – Active, online relational catalog
The description of the database and its contents represented at the logical level in tabular format and can be queried using the database language.
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Rule 5 – Comprehensive Data sub-language
At least one supported language must have a well defined syntax and must be comprehensive. It must support data definition, manipulation, integrity rules, authorization, and transactions.
Rule 6 – View updating rule
All views that are updatable an be updated through the system.
Rule 7 – Set-level insertion, update, and deletion
The DBMS also support set-level inserts, updates, and deletes.
Rule 8 – Physical data independence
Application programs and adhoc programs are logically unaffected when physical access methods or storage structures are altered.
Rule 9 – Logical data independence
Application programs and adhoc programs are logically unaffected, when changes are made to the table structures.
Rule 10 – Integrity Independence
The database language must be able of define integrity rules. These rules must be stored in online catalog and cannot be bypassed.
Rule 11 – Distribution Independence
Application programs and adhoc requests are logically unaffected when data is first distributed/redistributed.
Rule 12 – Nonsubversion
It must not be possible to bypass the integrity rules defined through the database language by using lower-level language.
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