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Explain & state the Codd’s 12 rules tutorials.

  • Ted Cpdd was PhD and working with IBM as Mathematical Programmer, invented the Relational Model for Database Management.

  • In Early 1970’s he worked on data arrangement theories and published White Paper on DBMS. Ted Codd presented 12 rules that are database must obey if it is to be considered truly relational.

 

The following is the Codd’s 12 rules –

 

1)     Information rules:- All information in a relational database is represented explicitly of the logical level and in exactly one way by values in tables.

2)     Guaranteed Access rule:- Since every value is represented exactly in same way at atomic level, hence access to the data is guaranteed. Moreover data is represented at the smallest possible level.

3)     Systematic treatment of null values:- Null values are supported in fully relational DBMS representing missing information and inapplicable information in a systematic way, independent of the data type.

4)     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 that authorized users can apply the same relational language to its interrogation as they apply to the regular data.

5)     Comprehensive data sub language rule:- A relational system may support several languages and various modes of terminal use. Thus, database language must be divided into sub languages e.g. DDL & DML.

6)     View updating rule:- Views that are updateable theoretically must be updateable by system also.

7)     High level insert, update & delete:- Database languages should possess high level commands on operating the database so that it inserts many other commands such as insert, update and delete.

8)     Physical data independence:- Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representations or access method.

9)     Logical data independence:- Application programs and terminal when information preserving changes of any kind that theoretically permit unimpairment are made to the base tables.

10)  Integrity independence:- These are so many integrity constraints in SQL that it should not interfere with each other. They must be independent.

11)  Distribution independence:- A relational DBMS has distribution independence.

12)  No subversions rule:- Since each record is represented at lower level in atomic form, so no integrity constraint can be by passed. For any operation those constraints must be checked.

 


 

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