Codd’s Rule:




The relational model of database systems was invented by Dr Edgar F. Codd. Dr Edgar F. Codd also introduced 12 rules that can be applied on the database systems; these rules mange the data that is stored using the relational capabilities. These rules are used to test or check the concept of DBMS against the relational model. The Codd’s rules are as follows:




Rule 0

The rule 0 is called the foundational rule. The foundational rule says that the system must be capable of managing the database through the relational capabilities.

Rule 1

Rule one is called information rule. The information rule says that the information should be represented in the cells of the table as stored data. Everything must be stored in table format. This information can be metadata.

Rule 2

The rule 2 is called Guaranteed Access Rule. This rule says that the value should be guaranteed an access with the combination of table name, primary key, and attribute name. The primary key is the row value, the table name is the name of the table and attribute name is the column value. Pointers can also be used to access the data.

Rule 3

The rule 3 is called systematic treatment of Null value. This rule says that a semantic and uniform treatment must be given to the null values in a database. A null value can be considered to be as data is missing, or the data is unknown or the data is not applicable. Therefore, this rule is very important.

Rule 4

The rule 4 is called Active online Catalog. This rule says that the database must be stored in the online catalog. This is known as data dictionary.

Rule 5

The rule 5 is called comprehensive data sub language rule. This rule says that the database can only be accessed by a specific language. This language has the linear syntax and support the definition of data and the manipulation of data.




Rule 6

The rule 6 is called view updating rule. This rule says that the database must be updated by the system.

Rule 7

The rule 7 is called high level insert, update, and delete rule. This rule says that insertion, updation and deletion must be supported by the database.

Rule 8

The rule 8 is called physical data independence. This rule says that the data that is stored in database should be independent of applications.

Rule 9

The rule 9 is called logical data independence. This rule says that the logical data in the database must be free of the views of users.

Rule 10

The rule 10 is called integrity independent rule. This rule says that the data that is stored in database should be independent of applications. All the constraints of integrity can be modified without the change in application independently.

Rule 11

The rule 11 is called distribution independence rule. This rule says that the data can be distributed among different locations. This rule can also be considered as the foundation of distributed database systems.




Rule 12

The rule 12 is called non subversion rule. This rule says that the interface cannot be subverted if the system does not have any interface for the low level records.