Dr. E. F. Codd's rules for RDBMS

DR. E. F. Codd rules

Rule 1:- All data should be stored and presented in table form.

Rule 2:- All data should be accessible without ambiguity. This can be accomplished through a combination of the table name, primary key, and column name.

Rule 3:- Mostly database implementation support the concept of not null field constraints that prevents null values in a specific table column.   

Rule 4:- A relational database must provide access to its structure through the same tools that are used to access the data.

Rule 5:- The database must support at least one language that includes functionality for data definition, data manipulation, data integrity, transaction control.   

Rule 6:- Data can be presented in the different logical forms called views. Each view should support the same full range of data manipulation that you can directly access to a table. But modification is not allowed here.

Rule 7:- Data can be retrieved from a relational database in sets constructed of data from multiple rows or multiple table. This rule states that insert, update and delete operation should be supported for any retrievable set rather than just for a single row in a single table.

Rule 8:- The user is isolated from the physical method of storing and retrieving information from the database.

Rule 9:- how data is viewed should not be changed when the logical structure of the database changes.

Rule 10:- The database should be support constraints on user input that maintain database integrity. Data integrity is part of the data definition language in SQL.

Rule 11:- User can not able to see data that how to data distributed over the various location.

Rule 12: There should be no way to modify the database structure or schema other than through the multiple row database language.  For more information