E. F. Codd’s 12 Rules by anil nain 9416077273

E. F. Codd’s 12 Rules by anil nain 9416077273


E. F. Codd has defined twelve rules that should be satisfied by any DBMS to be benchmarked as a RDBMS. These twelve rules are the guidelines on which all the RDBMS like ORACLE, INGRES, SYBASE, INFORMIX are based.
Rule One: The Information Rule
All information in a relational database is represented explicitly at the logical level and in exactly one way – by values in tables.
Rule Two: The Guaranteed Rule
Each and every datum in a relational database is guaranteed to be logically accessible by resorting to a combination of table name, primary key value and column name.
Rule Three: Systematic Treatment of Null Values
Null values are supported for representing missing information and inapplicable information in a systematic way independent of data type.
Rule Four: 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 date.
Rule Five: Comprehensive Data Sub-language Rule
A relational system may support several languages and various modes terminal use. However, there must be at least one language whose statements can express all of the following:
Data Definition, View Definition, Data Manipulation, Integrity constraint, Authorization, Transaction Boundaries.
Rule Six: View Updating Rule
All views that are theoretically updateable are also updateable by the system.
Rule Seven: High-level Insert, Update, and Delete
The capability of handling a base relation or a derived relation as a single operand applies not only to the retrieval of the data but also to the insertion, updation and deletion.
Rule Eight: Physical Data Independence
Application programmes and terminal activities remain logically unimpaired whenever any changes are made in either storage representation or access methods.
Rule Nine: Logical Data Independence
Application programmes and terminal activities remain logically unimpaired when information-preserving changes of any kind that theoretically permitted modifications are made to the base tables.
Rule Ten: Integrity Independence
Integrity constraints specific to a particular relational database must be definable in the relational data sub-language and storable in the catalogue, not in the application programmes.
Rule Eleven: Distribution Independence
The data manipulation data sub-language of a Relational DBMS must enable application programmes and enquires to remain logically the same whether data is physically centralized or distributed.


Rule Twelve: Non-Subversion Rule
If a Relational system has a low level language, that low level cannot be used to subvert or bypass the integrity rules and constraints expressed in the higher-level relational languages.
E. F. Codd’s 12 Rules by anil nain 9416077273