Codd's Rules are a set of principles proposed by Dr. Edgar F. Codd, the father of relational databases, to define the characteristics of a true relational database management system (RDBMS). These rules provide a framework for evaluating the quality and capabilities of RDBMS products.
The 12 Rules
Foundation Rule: All information in the database must be represented in the form of tables.
Rule of Primary Key: Each table must have a primary key, a unique identifier for each row.
Rule of First Normal Form: Each column in a table must contain atomic values, meaning each cell should contain a single value, not a set of values.
Rule of Second Normal Form: A table is in second normal form if it is in first normal form and all non-key attributes are dependent on the entire primary key.
Rule of Third Normal Form: A table is in third normal form if it is in second normal form and there are no transitive dependencies between non-key attributes.
Rule of Boyce-Codd Normal Form (BCNF): A table is in BCNF if every determinant is a superkey.
Rule of Null Values: The system must be able to represent missing or inapplicable data using null values.
Rule of Active Domain: Each column in a table must have a defined domain, which specifies the allowable values for that column.
Rule of Close World Assumption: The system must assume that all information in the database is complete.
Rule of Guaranteed Access: The system must provide guaranteed access to all information in the database.
Rule of View Updating: The system must support the definition and manipulation of views, which are virtual tables derived from other tables.
Rule of Physical Data Independence: The system must be able to change the physical storage structure without affecting the logical view of the data.
Why Are Codd's Rules Important?
Data Integrity: Codd's rules help ensure data consistency and accuracy by preventing anomalies and redundancy.
Data Independence: They promote physical data independence, allowing changes to the underlying storage structure without affecting the application.
Efficiency: Adhering to Codd's rules can lead to more efficient database operations.
Standardization: They provide a common framework for comparing and evaluating different RDBMS products.
Understanding the Rules in Detail
Rules 1-3: These foundational rules establish the basic structure of a relational database. They ensure that data is organized in a tabular format and that each row is uniquely identifiable.
Rules 4-6: These rules deal with normalization, which is the process of organizing data to minimize redundancy and improve data integrity. By adhering to these rules, database designers can avoid anomalies such as update anomalies, insertion anomalies, and deletion anomalies.
Rules 7-10: These rules address the handling of missing data, data types, and access control. They ensure that databases can represent incomplete information and provide secure access to data.
Rules 11 and 12: These rules relate to the logical and physical aspects of a database. They ensure that users can view data in a way that is meaningful to them and that changes to the underlying storage can be made without affecting the application.
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