Codd’s Rules in DBMS
Codd’s Rules is developed by E.F.Codd for RDBMS in 1970. It is also known as Codd’s 12 Rules. The Codd’s Rules are given as follows:
Explain Codd’s Rule in Detail:
Rule 1: Information Representation
In a relational database model, all information should be explicitly and logically represents by entering the data values in the form of tables. The information such as view and column names should be in table form. The Datastore in the data dictionary should also be in tabular form.
Rule 2: Guaranteed Access
This rule refers to the fact that a table can be taken as a storage structure and at the intersection of each column and row, there will necessarily be only one specific value of data item (or null). So, every value of data item must be logically addressable by using a combination of table_name, primary-key-value and the column-name.
Rule 3: Systematic Treatment of Null Values
In RDMS, null values support the representation of missing and inapplicable information only. It must have a consistent method for representing null values.
Rule 4: Database Description Rule
The description of the database stored and maintains in the form of tables. This allows users with appropriate authority to query information using the same language. Stored implies that a data dictionary should be present within the RDBMS. It constructs out of tables that can examine by using the structured query language (SQL).
Rule 5: Comprehensive Data Sub-Language
The RDBMS must be completely manageable through its extension of SQL. The SQL should support Data Definition, Views, Data Manipulation, Integrity Constraints, and Transaction Boundaries.
Rule 6: View Updating
Any view can define using a combination of base tables and it updates theoretically. It must also be capable of being updated by the RDBMS.
Rule 7: High-Level Update, Insert, Delete
An RDBMS must do more than just be able to retrieve relational data sets. It must also be possible to insert, update and delete data items from the relational set.
Rule 8: Physical Data Independence
It refers to the ability to modify the schema. It follows at the physical level without causing application programs. However, it makes to change physical storage representation or access methods doesn’t require changes to make to the application programs uses for manipulating data in the tables.
Rule 9: Logical DaIndependence
Logical Data Independence refers to the ability to modify the conceptual schema without causing any changes in the schema followed at the view level.
Rule 10: The Distribution Rule
An RDBMS must have distribution independence. Thus it must make it possible for the database to be distributed across multiple computers even though they are having heterogeneous platforms both for hardware and operating system. So, it is one of the most attractive aspects of RDBMS.
Rule 11: Non-Subversion
If the RDBMS supports facilities allowing application programs to operate on a table a row at a time, then an application program uses this type of database access. It prevents bypassing the entity-integrity constraints that may be defined for the database.
Rule 12: Integrity Rule
Integrity constraints specifies that a particular relational database. It must be definable in SQL and some other data sub-language.