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What are CODD’S 12 Rules in Database System?

CODD’s 12 rules are set of designed rules developed by Dr Edgar F. Codd which is used for defining what is needed from a database management system in order for it to be regarded as relational database management system

Rule 1: Information Rule

The data stored in a database, it could be user data or metadata, it must be a value of some table cell. Everything in a database must be stored in a table format.

Rule 2: Guaranteed Access Rule

Every single data element (value) is guaranteed to be accessible logically with a grouping of table-name, primary-key (row value), and attribute-name (column value). No other way, such as pointers, can be used to access data.

Rule 3: Systematic Treatment of NULL Values
The NULL values in a database must be given a systematic or organized and consistent treatment. This is a very vital rule because a NULL can be translated as one the following: data is missing, data is not known, or data is not applicable.

Rule 4: Active Online Catalog

The structure description or explanation of the entire database must be stored in an online catalog, called data dictionary, which can be accessed by approved users. Users can make use of the same query language to access the catalog which they normally use to access the database itself.

Rule 5: Comprehensive Data Sub-Language Rule

A database can only be accessed using a language possessing linear syntax that supports data definition, data manipulation, and transaction management operations. This language can be used directly or by the use of some application. If the database permits access to data without any assist of this language, then it is regarded as a violation.

Rule 6: View Updating Rule

All the views of a database, which can theoretically be updated, must also be updatable by the system.

Rule 7: High-Level Insert, Update, and Delete Rule

A database must support high-level insertion, updation, and deletion. This must not be restricted to a single row, i.e, it must also support union, intersection and minus operations to yield sets of data records.

Rule 8: Physical Data Independence

The data stored in a database must not depend on the applications that access the database. Any change or amend made in the physical structure of a database must not have any effect on how the data is being accessed by external applications.

Rule 9: Logical Data Independence

The logical data in a database must be independent of its user’s view (application). Any change or amend made in logical data must not have any effect or impact on the applications using it. For instance, if two tables are merged or one is split into two different tables, there should be no impact or effect on the user application. This is one of the most complicated rules to employ.

Rule 10: Integrity Independence

A database must not depend on the application that uses it. All its integrity constraints can be autonomously modified without the need of any change or amendment in the application. This rule makes a database independent of the front-end application and its interface.

Rule 11: Distribution Independence

The end-user must not be able to notice that the data is distributed over different locations. Users should always get the feeling that the data is located at one site only. This rule has been regarded as the foundation of distributed database systems.

Rule 12: Non-Subversion Rule

If a system has an interface that provides access to low-level records, then the interface must not be able to undermine the system and bypass security and integrity constraints.

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