February 03, 2020
Amitraj
Codd's Rule for Relational DBMS
E.F Codd was a Computer Scientist who invented the Relational model for Database management. Based on relational model, the Relational database was created. Codd proposed 13 rules popularly known as Codd's 12 rules to test DBMS's concept against his relational model.
Codd's rule actualy define what quality a DBMS requires in order to become a Relational Database Management System(RDBMS). Till now, there is hardly any commercial product that follows all the 13 Codd's rules. Even Oracle follows only eight and half(8.5) out of 13. The Codd's 12 rules are as follows.
Rule zero
This rule states that for a system to qualify as an RDBMS, it must be able to manage database entirely through the relational capabilities.
Rule 1: Information rule
All information(including metadata) is to be represented as stored data in cells of tables. The rows and columns have to be strictly unordered.
Rule 2: Guaranted Access
Each unique piece of data(atomic value) should be accesible by : Table Name + Primary Key(Row) + Attribute(column).
NOTE: Ability to directly access via POINTER is a violation of this rule.
Rule 3: Systematic treatment of NULL
NULL value in database must only correspond to missing, unknown or not applicable values.
Rule 4: Active Online Catalog
Structure of database must be stored in an online catalog which can be queried by authorized users.
Rule 5: Powerful and Well-Structured Language
One well structured language must be there to provide all manners of access to the data stored in the database. Example: SQL, etc. If the database allows access to the data without the use of this language, then that is a violation.
Rule 6: View Updation Rule
All the view that are theoretically updatable should be updatable by the system as well.
Rule 7: Relational Level Operation
There must be Insert, Delete, Update operations at each level of relations. Set operation like Union, Intersection and minus should also be supported.
Rule 8: Physical Data Independence
The physical storage of data should not matter to the system. If say, some file supporting table is renamed or moved from one disk to another, it should not effect the application.
Rule 9: Logical Data Independence
If there is change in the logical structure(table structures) of the database the user view of data should not change. Say, if a table is split into two tables, a new view should give result as the join of the two tables. This rule is most difficult to satisfy.
Rule 10: Integrity Independence
Integrity constraints modified at database level should not enforce modification at application level.
Rule 11: Distribution Independence
Distribution of data over various locations should not be visible to end-users.
Rule 12: Nonsubversion Rule
Low level access to data should not be able to bypass integrity rule to change data.
E.F Codd was a Computer Scientist who invented the Relational model for Database management. Based on relational model, the Relational database was created. Codd proposed 13 rules popularly known as Codd's 12 rules to test DBMS's concept against his relational model.
Codd's rule actualy define what quality a DBMS requires in order to become a Relational Database Management System(RDBMS). Till now, there is hardly any commercial product that follows all the 13 Codd's rules. Even Oracle follows only eight and half(8.5) out of 13. The Codd's 12 rules are as follows.
Rule zero
This rule states that for a system to qualify as an RDBMS, it must be able to manage database entirely through the relational capabilities.
Rule 1: Information rule
All information(including metadata) is to be represented as stored data in cells of tables. The rows and columns have to be strictly unordered.
Rule 2: Guaranted Access
Each unique piece of data(atomic value) should be accesible by : Table Name + Primary Key(Row) + Attribute(column).
NOTE: Ability to directly access via POINTER is a violation of this rule.
Rule 3: Systematic treatment of NULL
NULL value in database must only correspond to missing, unknown or not applicable values.
Rule 4: Active Online Catalog
Structure of database must be stored in an online catalog which can be queried by authorized users.
Rule 5: Powerful and Well-Structured Language
One well structured language must be there to provide all manners of access to the data stored in the database. Example: SQL, etc. If the database allows access to the data without the use of this language, then that is a violation.
Rule 6: View Updation Rule
All the view that are theoretically updatable should be updatable by the system as well.
Rule 7: Relational Level Operation
There must be Insert, Delete, Update operations at each level of relations. Set operation like Union, Intersection and minus should also be supported.
Rule 8: Physical Data Independence
The physical storage of data should not matter to the system. If say, some file supporting table is renamed or moved from one disk to another, it should not effect the application.
Rule 9: Logical Data Independence
If there is change in the logical structure(table structures) of the database the user view of data should not change. Say, if a table is split into two tables, a new view should give result as the join of the two tables. This rule is most difficult to satisfy.
Rule 10: Integrity Independence
Integrity constraints modified at database level should not enforce modification at application level.
Rule 11: Distribution Independence
Distribution of data over various locations should not be visible to end-users.
Rule 12: Nonsubversion Rule
Low level access to data should not be able to bypass integrity rule to change data.
