EF Codd Rules : Introduction
- Edgar Frank Codd(EF Codd) was a computer scientist who invented the concept and standard of Relational Database Model. According to him, a database management system can be termed as an RDBMS only if it designed according to the 13 rules and follows them as well. These are known as EF Codd Rules in DBMS.
- Software systems are categorized according to the number of EF Codd rules these software follows.
- There are 13 rules(0 to 12) all which are discussed in detail below.
EF Codd Rules : The Discussion
- Rule-0 : The “Foundation” Rule
Explanation : This rule ensure that for a software to qualify and act as an RDBMS, the system must manage the database through its relational capabilities.
- Rule-1 : The “Information” Rule
Explanation : The information of data in the relational database is stored in rows and column in the form of tables.
- Rule-2 : The “Guaranteed Access” Rule
Explanation : Each and every atomic value is accessible by using the combination of Name of table(row), Primary-Key(column) and Name of attribute. Use of concept of pointers is not allowed.
- Rule-3 : The “Systematic Treatment Of NULL Values” Rule
Explanation : Support for NULL value acceptance is checked using this rule. It means table can have a missing or no value field and DBMS must support it to be called as an RDBMS.
- Rule-4 : The "Dynamic Online Catalogue” Rule
Explanation : The description of structure of the whole database needs to be stored online which only can be accessed by authorized or permissible users/personals.
- Rule-5 : The “Comprehensive Data Sub-language” Rule
Explanation : Multiple language support is required. It means, relational database languages such as SQL, OCL, TQL can be used, only if they are able to manipulate the data. Manipulation includes, creation of database, implementation, security and data retrieval. There must be support of at least one language to cater all the above mentioned request.
- Rule-6 : The “View Updating” Rule
Explanation : The number of possible views of a database system which can be manually altered or updated, this rule requires the system to perform this task automatically too.
- Rule-7 : The “High-Level Insert, Update & Delete” Rule
Explanation : This rule ensures that the database system must be able to support the insertion, deletion and updation function with the help of any query language such as SQL.
- Rule-8 : The “Physical Data Independence” Rule
Explanation : Any changes or alteration in the physical structure of the database must not affect or change or manipulate the data stored in the database.
- Rule-9 : The “ Logical Data Independence” Rule
Explanation : Any changes or alterations in the logical structure of the database(such as changes in view of tables) must not affect or change the end user’s view and ability to interact with the database.
- Rule-10 : The “ Integrity Independence” Rule
Explanation : Databases must need to support integrity constraints such as primary key value must be not NULL and other constraints such referential integrity constraint must be followed.
- Rule-11 : The “ Distribution Independence” Rule
Explanation : The application view database known to user must have an abstract view. It means for request of data made by users, the user should feel that data is getting retrieved from a single location rather than multiple location. There must not be any delay while retrieving data.
- Rule-12 : The “Non-Subversion” Rule
Explanation : If database system allows users to access the low level views of database files, one cannot violate rules and constraints defined for the database files by producing any changes to the database files.
Note : For further details on EF Codd Rules, kindly visit THIS.