Day 14: Codd's 12 Rules

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Today we are going to cover the Codd's 12 Rules.

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CODD's 12 RULES - Relational database is the database in which the data is in the form of tables basically. However, it is not just that. Codd's 12 rules was proposed by Dr. E.F.Codd and thus it is named as Codd's rules. He introduces 12 rules for a DBMS to be a relational database. However, a database can be relational database if it satisfies atleast 6 rules from these rules. The rules are as follows -

  • INFORMATION RULE - The information rule states that every information in the database is stored in the form of tables only which is combination of rows and columns. The information is not stored in any other form but only in tabular form.
  • GUARANTEED ACCESS RULE - This rule states that each element in the database will be accessed guaranteed either through table name, primary key or the attributes.Access data logically i.e. by referencing a table's key value or column, and it is not accessed by physical location. For example, it cannot be accessed through referencing 2nd row of table, but can be by referencing Emp_ID in Employee table.
  • SYSTEMATIC TREATMENT OF NULL VALUES - This rule states that in any table if there is not any value filled in that, so there should include null value. A null value is not like blank space or 0. If no value is there in the table, then null value should be there.
  • ACTIVE ONLINE CATALOG - This rule states that the database structure should be kept in an online catalog so that the database administrator can manage its queries.
  • COMPREHENSIVE DATA SUB-LANGUAGE RULE - This rule states that every database must have its own language for the database management. Generally, mostly RDBMS uses SQL language(Structured-Query Language).
  • VIEW UPDATING RULE - View refers to virtual relation which is derived from one or more base relations. In this rule, it states that there may be different views and the system should automatically update the views which are created.
  • HIGH LEVEL, INSERT, UPDATE AND DELETE - RDBMS must support the operations such as insert, update and delete. Moreover, it should support algebraic operations(Selection, Projection, Join) and Set Operations(Union, Intersection, Division, and Difference).
  • PHYSICAL DATA INDEPENDENCE - This rule states that if there changes occur in physical storage, then the user view or the application should not get affected by that. 
  • LOGICAL DATA INDEPENDENCE -  This rule states that if there changes occurs in logical level, then the application should not get affected. If we do changes in our tables, then the application should not get affected by that.
  • INTEGRITY INDEPENDENCE - Data integrity means the consistency and the accuracy of the data. This rule states that if there any insertion is done then the integrity should not be sacrificed.
  • DISTRIBUTION INDEPENDENCE - This rule states that the end user is unaware about the application distribution. The end user is not able to understand the functioning and is limited to it's view. The data can be stored centrally or distributed but user should not be capable of that to find out.
  • NON SUBVERSION RULE - This rule states that if the database is using a particular language then it should not use other language for any transaction. Foe example, if an RDBMS uses SQL language for its operations then the SQL is used only and not any other language instead of SQL. 
So the above are Codd's 12 rules for RDBMS in a very simple words for your understandability. 



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