Codd's 12 Rule

1. Foundation Rule

A relational database management system must manage its stored data using only its relational capabilities.

2. Information Rule

All information in the database should be represented in one and only one way - as values in a table.

3. Guaranteed Access Rule

Each and every datum (atomic value) is guaranteed to be logically accessible by resorting to a combination of table name, primary key value and column name.

4. Systematic Treatment of Null Values

Null values (distinct from empty character string or a string of blank characters and distinct from zero or any other number) are supported in the fully relational DBMS for representing missing information in a systematic way, independent of data type.

5. Dynamic On-line Catalog Based on the Relational Model

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.

6. Comprehensive Data Sublanguage Rule

A relational system may support several languages and various modes of terminal use. However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings and whose ability to support all of the following is comprehensible:

a. data definition

b. view definition

c. data manipulation (interactive and by program)

d. integrity constraints

e. authorization

f. transaction boundaries (begin, commit, and rollback).

7. View Updating Rule

All views that are theoretically updateable are also updateable by the system.

8. High-level Insert, Update, and Delete

The capability of handling a base relation or a derived relation as a single operand applies nor only to the retrieval of data but also to the insertion, update, and deletion of data.

9. Physical Data Independence

Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage...