Dr. E. F. Codd's 12 rules

http://www.studytonight.com/dbms/codd-rule.php

http://maaulik.0fees.net/resources/E_F_Codd_rules_4_RDBMS.htm

Dr. E. F. Codd's 12 rules

For defining a fully relational database

A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd. Most popular commercial and open source databases currently in use are based on the relational model.

A short definition of an RDBMS may be a DBMS in which data is stored in the form of tables and the relationship among the data is also stored in the form of tables.

E.F. Codd, the famous mathematician has introduced 12 rules for the relational model for databases commonly known as Codd's rules. The rules mainly define what is required for a DBMS for it to be considered relational, i.e., an RDBMS. There is also one more rule i.e. Rule00 which specifies the relational model should use the relational way to manage the database. The rules and their description are as follows:-

Rule 0: Foundation Rule

A relational database management system should be capable of using its relational facilities (exclusively) to manage the database.

Rule 1: Information Rule

All information in the database is to be represented in one and only one way. This is achieved by values in column positions within rows of tables.

Rule 2: Guaranteed Access Rule

All data must be accessible with no ambiguity, that is, Each and every datum (atomic value) is guaranteed to be logically accessible by resorting to a combination of table name, primary key value and column name.

Rule 3: Systematic treatment of null values

Null values (distinct from empty character string or a string of blank characters and distinct from zero or any other number) are supported in the fully relational DBMS for representing missing information in a systematic way, independent of data type.

Rule 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 authorized users can apply the same relational language to its interrogation as they apply to regular data. The authorized users can access the database structure by using common language i.e. SQL.

Rule 5: Comprehensive Data Sublanguage Rule

A relational system may support several languages and various modes of terminal use. However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings and whose ability to support all of the following is comprehensible:

data definitionview definitiondata manipulation (interactive and by program)integrity constraintsauthorizationTransaction boundaries (begin, commit, and rollback).

 

Rule 6: View Updating Rule

All views that are theoretically updateable are also updateable by the system.

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

The system is able to insert, update and delete operations fully. It can also perform the operations on multiple rows simultaneously.

Rule 8: Physical Data Independence

Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representation or access methods.

Rule 9: Logical Data Independence
Application programs and terminal activities remain logically unimpaired when information preserving changes of any kind that theoretically permit unimpairment are made to the base tables.

Rule 10: Integrity Independence
Integrity constraints specific to a particular relational database must be definable in the relational data sublanguage and storable in the catalog, not in the application programs.

Rule 11: Distribution Independence
The data manipulation sublanguage of a relational DBMS must enable application programs and terminal activities to remain logically unimpaired whether and whenever data are physically centralized or distributed.

Rule 12: Nonsubversion Rule
If a relational system has or supports a low-level (single-record-at-a-time) language, that low-level language cannot be used to subvert or bypass the integrity rules or constraints expressed in the higher-level (multiple-records-at-a-time) relational language.

 

Note that based on these rules there is no fully relational database management system available today. In particular, rules 6, 9, 10, 11 and 12 are difficult to satisfy.

 

REFERENCES

Codd, E. (1985). "Is Your DBMS Really Relational?" and "Does Your DBMS Run By the Rules?" ComputerWorld, October 14 and October 21. Elmasri, R., & Navathe, S. (1994). Fundamentals of Database Systems. 2nd ed. Redwood City, CA: The Benjamin/Cummings Publishing Co. pp. 283 – 285.

Oracle Codd's 12 Rules

http://psoug.org/reference/codds_rules.html

 

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

Rule 2: Guaranteed Access    Each and every datum (atomic value) 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 3: Systematic Treatment of Null Values    Null values (distinct from the empty character string of blank characters and distinct from any zero or other numbers) are supported in fully relational DBMS for representing missing information and inapplicable information in a systematic way.    

Rule 4: Dynamic Online 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.    

Rule 5: Comprehensive Data Sub-language    A relational system may support several languages and various modes of terminal use (for example, the fill-in-the-blanks mode). However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings, that is comprehensive in supporting all of the following items:Data DefinitionView DefinitionData manipulation (interactive and by program)Integrity ConstraintsAuthorizationTransaction boundaries (begin, commit, and rollback)    

Rule 6: View Updating    All views that are theoretically updateable are also updateable by the system.    

Rule 7: 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 data but also to the insertion, update, and deletion of data.    

Rule 8: Physical Data Independence    Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representations or access methods.    

Rule 9: Logical Data Independence    Application programs and terminal activities remain logically unimpaired when information-preserving changes of any kind that theoretically permit unimpairment are made to the base tables.    

Rule 10: Integrity Independence    Integrity constraints specific to a particular relational database must be definable in the relational data sub-language and storable in the catalog, not in the application programs.    

Rule 11: Distribution Independence    A relational DBMS has distribution dependence.    

Rule 12: Nonsubversion    If a relational system has a low-level (single record at a time) language, that low level cannot be used to subvert or bypass the integrity rules and constraints expressed in the higher-level relational language (multiple records at a time).