Codds Twelve Rules

Codd’s twelve rules for a system to be classified as a (fully relational) DBMS

  1. Information Rule – Information is to be represented as data stored in cells
  2. Guaranteed Access Rule- Every row must be accessible using a combination of Table name+Primary key+Column name
  3. Nulls must be used in a consistent manner -Irrespective of the datatype of the column
  4. Metadata should be stored as relational tables and must be accessible using SQL constructs
  5. The data access language must provide all means of access and must be the only means of access
  6. All views that may be updateable must be updateable
  7. There must be set level insert, updates and deletes – Here is an example of a set level delete:

    delete from payroll_transaction where transaction_id in
    (select
    transaction_id from #t_EmpPayrollTrans)

  8. Physical data independence
  9. Logical data independence
  10. Integrity rules should be stored in the data dictionary
  11. Distribution independence
  12. Non subversion rule
  13. (or Rule 0) The system itself must use its relational facilities exclusively to manage the database
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