Codd rule of rdbms

CODD’S RULE FOR RDBMS (Relational Database Management System)

It is the rules for dbms to be an rdbms. There are 12 rules (at least 6 must be followed to be called as an rdbms)

RULE 1: Information Rule

Data must be organized in form of table because this is the most convenient way to organize and interpret the data.

RULE 2: Access Rule

It must ensure that any authorized user having access permission will never be denied of using the data file and they should be able to access only what they are allowed to.

RULE 3: Data Language

It must support language which have operations related to structures and data manipulation.

RULE 4: View Language/ Manipulation/ Update

It must be support operation related to creation, manipulation etc. It creates additional security between the end users.

*RULE 5: Physical Independence

It’s about changing the physical media or changing the access of physical media. It shouldn’t require any change in the program.

*RULE 6: Logical Independence

Here, the deletion, drop, update or alter don’t requires any change in the program i.e. we can change structure without change the program.

RULE 7: Integrity (Constraints) Independence

Whichever constraints are applied to maintain data integrity, we should be able to change it without changing the program/ structures.

 eg: changing of primary key with alternative key.

RULE 8: Subversion Rule

There shouldn’t be any sub-version of the system.

Undue/ unauthorized use of the system must be prevented.

One shouldn’t bypass any other rule.

RULE 9: Distribution Rule

Any dbms should be able to distribute part of it, when required.

It should be able to distribute data, over no. of machine when required, based on their geography (location) or requirement.

*RULE 10: Data Description Catalogue

It is a kind of dictionary in which storage catalogues and attributes are present.

This rule says that

all the data items in the database,

the storage structure created to hold the data in the database, information about them i.e. attributes,

structures etc

must be stored. This storage is referred to as data description catalogue or data dictionary.

For any dbms to be termed as an rdbms, it must support data dictionary/ catalogue’s concept.

*RULE 11: High Level Operations Insert, Delete, Updates

It must be supported by all the DBMSs to be termed as an RDBMS.

RULE 12: Proper Treatment of NULL values

The null value is taken from same domain if it is allowed.

[ * are major rules]

NOTE: BLOB IS Binary Large Object used to store image, video files, etc.