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Codd's Twelve Rules
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  1. The information rule: This rule require all information to be represented as data values in the rows and column of table.
  2. The guaranteed access rule:Every data value in a relational database should be logically accessible by specifying a combination of table name and column name.
  3. Systematic treatment of NULL values: DBMS support NULL values ,in case when user leave the column in the table.

  4. Active online catalog based on relational model: DBMS maintain system catalog. System catalog is a collection of system table.
  5. The comprehensive data sublanguage rule:
  6. System must support following functions :

    1. Data definition
    2. View definition
    3. Data manipulation operation
    4. Security and integrity constraints
    5. Transaction management operation


  7. The view update rule: All views that are theoretically updated must be updated by the system.
  8. High level insert, update and delete: Means update at a time many rows values. Data are treated as set ,which are easily delete ,& update and insert.
  9. Physical data independence: Application programs must remain unimpaired when any changes are made in storage representation or across methods.
  10. Logical data independence: Changes should not affect the user's ability to work with the data.
  11. Integrity independence: Integrity constraints must be storable in the system catalog.
  12. Distribution independence: Database must allow manipulation of distributed data located on different computer system.
  13. Nonsubversion rule: This rule state that different language bypass the integrity rule and constraints.
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