D R. E.F.C ODD ’ S R ULES FOR RDBMS Dr. E.F.Codd is an IBM researcher who first developed the relational data model in 1970.Dr. Codd published a list of 12 rules that define ideal relational database and provide a guideline for design of all relational database system. A.P.M.S

Rule 1: The Information Rule- All the information in the database should be represented in the table form. Rule 2: The Guaranteed Access Rule- All data should be accessible without ambiguity. This can be accomplished through combination of the table name,primary key and column name Rule 3: Systematic Treatment of Null Values- The DBMS must allow each field to remain null. The null can be stored in any field of any data type. Null values (distinct from the empty character string or a string of blank characters and distinct from zero or any other number) are supported in fully relational DBMS for representing missing information and inapplicable information in a systematic way, independent of data type. A.P..S

Rule 4: Dynamic On-line Catalog Based on the Relational Model- The data base description is represented at the logical level in the same way as- ordinary data, so that authorized users can apply the same relational language to its interrogation as they apply to the regular data. The authorized users can access the database structure by using common language i.e. SQL. Rule 5: Comprehensive Data Sublanguage Rule- The system must support at least one relational language that has simple syntax and transaction management facilities. It can be used in the application as well as in the RDBMS systems. That sublanguage is comprehensive in supporting Data Definition, View Definition, Data Manipulation, Integrity Constraints and Authorization. A.P.M.S

Rule 6 : View Updating Rule- All views that are theoretically updatable are also updatable by the system. Not only can the user modify data, but so can the RDBMS when the user is not logged-in. Rule 7: High-level Insert, Update, and Delete- The system is able to insert, update and delete operations fully. It can also perform the operations on multiple rows simultaneously. Rule 8: Physical Data Independence- the user is isolated from the physical method of storing and retrieving information from the database. Changes to the physical storage structure must not require a change to an application based on the structure. A.P.M.S

Rule 9: Logical data independence - Changes to the logical level (tables, columns, rows, and so on) must not require a change to an application based on the structure. Rule 10: Integrity independence - All the Integrity constraints like primary key, unique key etc must be specified separately from application programs and stored in the catalog. The database language (like SQL) should support Constraints on user input that maintain database integrity. Rule 11: Distribution independence- the user should be totally unaware of whether or not the database is distributed. It means the parts of the table should be exist in multiple location. A.P.M.S

12) Rule 12: Non subversion Rule- If a relational system has a low-level (single-record-at-a-time) language, that low level cannot be used to subvert or bypass the integrity Rules and constraints expressed in the higher level relational language (multiple-records-at-a-time). A.P.M.S