1. Codd, the famous mathematician has introduce 12 rules for the relational model for
databases commonly known as Codd's rules. The rules mainly define what is required for
a DBMS for it to be considered relational , i.e., an RDBMS. There is also one more rule
i.e Rule00 which specifies the relational model should use the relational way to manage
the database. The rules and their description is as follows:-
Rule 000: A RDBMS system should be capable of using its relational facilities
(exclusively) to manage the database.
Rule 1: The information rule : All information in the database is to be represented in one
and only one way. This is achieved by values in column positions within rows of tables.
Rule 2 : The guaranteed access rule : All data must be accessible with no ambiguity.This
is achieved in the RDBMS by using the primary key concept.
Rule 3: Systematic treatment of null values : The DBMS must allow each field to remain
null. The null can be stored in any field of any datatype.
Rule 4: Active online catalog based on the relational model : The authorized users can
access the database structure by using common language i.e SQL.
Rule 5: The comprehensive data sublanguage rule : The system must support at least one
relational language that has simple syntax and transaction management facilities. It can
be used in the application as well as in the RDBMS systems.
Rule 6: The view updating rule : All views must be updatable by the system.
Rule 7: High-level insert, update, and delete : The system is able to insert, update and
delete operations fully. It can also perform the operations on multiple rows
simultenously.
Rule 8: Physical data independence : Changes to the physical storage structure must not
require a change to an application based on the structure.
Rule 9: Logical data independence : Changes to the logical level (tables, columns, rows,
and so on) must not require a change to an application based on the structure.
Rule 10: Integrity independence : All the Integrity constraints like primary key, uniques
key etc must be specified separately from application programs and stored in the catalog.
Rule 11: Distribution independence : The distribution of portions of the database to
various locations should be invisible to users of the database.
Rule 12: The nonsubversion rule : If the system provides a low-level (record-at-a-time)
interface, then that interface cannot be used to subvert the system, for example, bypassing
a relational security or integrity constraint.
Note:- Any database management system which fulfills 6 or more than 6 rules can be
considered as the RDBMS.
Maulin Thaker Codd's Rule
There are 13 (0 to 12) rules which were presented by Dr. E.F.Codd ,in June 1970,in ACM
(Association of Computer Machinery)
Rule 0. Relational Database management “A relational database management system
must use only its relational capabilities to manage the information stored in the database”.
Rule 1. The information rule All information in the database to be represented in one and
only one way, Namely by values in column positions within rows of tables.
Rule 2. Logical accessibility This rule says about the requirement of primary keys. Every
individual value in the database must be logically addressable by specifying the name of
table, column and the primary key value of the row.
Rule 3. Representation of null values The DBMS is required to support a representation

2. of "missing information and inapplicable information" (for example, 0 'Zero' is different
from other Numbers), This type of information must be represented by the DBMS in a
systematic way (For example Null Character ).
Rule 4. Catalog Facilities The system is required to support an on line, in line, relational
data access to authorized users by using their Query language.
Rule 5. Data Languages. The system must support a least one relational language (It may
support more than one relational language) that (a) has a linear syntax,
(b) can be used in two ways and within application programs,
(c) supports data operations security and integrity constraints, and transaction
management operations (commit).
Rule 6. View Updatability All views that are theoretically updatable must be updatable
by the system.
Rule 7. update and delete. The system must support INSERT, UPDATE, and DELETE
operators.
Rule 8. Physical data independence Changes to the physical level (how the data is stored,
whether in arrays or linked lists etc.) must not require a change to an application based on
the structure.
Rule 9. Logical data independence Changes made to tables to modify any data stored in
the tables must not require changes to be made to application programs. Logical data
independence is more difficult to achieve than physical data independence.
Rule 10. Integrity Constraints Integrity constraints must be specified separately from
application programs and stored in the catalog. It must be possible to change such
constraints when they are unnecessarily affecting existing applications.
Rule 11. Database Distribution The RDBMS may spread across more than one system
and across several networks, however the tables should appear in same manner to every
user like local users.
Rule 12. The Non Subversion rule If the system provides a low-level interface, then that
interface cannot be used to weaken the system (e.g.) bypassing a relational security or
integrity constraint.