Codd's rules or Codd's law are the set of 12 states which was developed by E.F. Codd in the year 1969-1970. Codd's law tells what is required from the database management system so that it can be considered relational.in other words, Codd's rules are rules for designing the RDBMS.

  • Rule 1: Information rule:-All the information has to be represented in only one way in the table
  • Rule 2:Guaranteed Access:-Every value in the table has to be accessible by the Table Name + Primary Key(Row) + Attribute(column).
  • Rule 3: Systematic treatment of NULL:-NULL values should be treated systematically
  • Rule 4: Active Online Catalog:-The catalog must be stored online
  • Rule 5: Powerful and Well-Structured Language: -A structured language should provide all access to the data which is stored in the database.
  • Rule 6: View Updation Rule:-All the view has to be updatable by the database system
  • Rule 7: Relational Level Operation:-There has to be the Insert, Delete, Update operations at every level of the relations
  • Rule 8: Physical Data Independence:-The changes in the Physical storage of the data should not affect the database system.
  • Rule 9: Logical Data Independence:-The changes in the logical structure of the database should not change the user view of the data.
  • Rule 10: Integrity Independence:-The Key and the Check constraints, the trigger, etc., should be stored in the Data Dictionary.
  • Rule 11: Distribution Independence: -A database should work correctly even if it is distributed across the network
  • Rule 12:Nonsubversion Rule:-If the low-level access has been allowed to a system; then it should not be able to subvert the integrity rules to alter the data.

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