- Codd’s rules are proposed by a computer scientist named Dr. Edgar F. Codd.
- he also invented the relational model for database management.
- These rules are made to ensure data integrity, consistency, and usability.
- This set of rules basically signifies the characteristics and requirements of RDBMS.
Codd’s Rules in DBMS*
Rule 1: The Information Rule
- All information, whether it is user information or metadata, that is stored in a database must be entered as a value in a cell of a table.
- Everything within the database is organized in a table layout.
*Rule 2: The Guaranteed Access Rule
- Each data element is guaranteed to be accessible logically with a combination of the table name, primary key (row value), and attribute name (column value).
- with proper column , row and table, u can access anything
Rule 3: Systematic Treatment of NULL Values*
Every Null value in a database must be given a systematic and uniform treatment.
Rule 4: Active Online Catalog Rule*
The database catalog, containing the metadata about the database, must be stored and accessed using the same RDBMS.
Rule 5: The Comprehensive Data Sublanguage Rule*
A crucial component of any efficient database system is its ability to offer an easily understandable data manipulation language that facilitates defining, querying, and modifying information within the database.
Rule 6: The View Updating Rule
All views that are theoretically updatable must also be updatable by the system.
Rule 7: High-level Insert, Update, and Delete*
A successful database system must possess the feature of facilitating high-level insertions, updates, and deletions that can grant users the ability to conduct these operations with ease through a single query.
Rule 8: Physical Data Independence*
Application programs and activities should remain unaffected when changes are made to the physical storage structures or methods.
Rule 9: Logical Data Independence*
Application programs and activities should remain unaffected when changes are made to the logical structure of the data, such as adding or modifying tables.
Rule 10: Integrity Independence
Integrity constraints should be specified separately from application programs and stored in the catalog. They should be automatically enforced by the database system.
Rule 11: Distribution Independence
The distribution of data across multiple locations should be invisible to users, and the database system should handle the distribution transparently.
Rule 12: Non-Subversion Rule*
If the interface of the system is providing access to low-level records, then the interface must not be able to damage the system and bypass security and integrity constraints.