Lesson 6	Normalization and Codd's 12 Criteria
Objective	Explain how Achieving Third Normal Form adheres to Codd's 12 Criteria.

Achieving Third Normal Form (3NF) and Its Relationship to Codd’s 12 Rules

The principles of Third Normal Form (3NF) and Codd’s 12 Rules share a common purpose: to ensure data integrity, consistency, and logical clarity within relational database systems. While normalization focuses on data structure and design, Codd’s rules define the system-level behavior that a true relational database should exhibit. This lesson connects how achieving 3NF complements and reinforces several of Codd’s key rules.

How 3NF Aligns with Codd’s Rules

3NF primarily addresses data redundancy and transitive dependencies, but its effects extend to broader relational principles. The following sections show how specific Codd rules benefit from a 3NF-compliant schema.

1. Rule 1 – Information Rule

All information in a relational database is represented explicitly at the logical level and in one way—through values in tables.

3NF Connection: By removing transitive dependencies, 3NF ensures that data is represented logically and unambiguously in tables. Each fact appears once, eliminating duplication and ambiguity.

2. Rule 2 – Guaranteed Access Rule

Every data item must be accessible by specifying a table name, primary key, and column name.

3NF Connection: Because 3NF enforces atomic, non-redundant data storage, every data item has a single point of access through its table and primary key, ensuring clarity and avoiding multiple dependency paths.

3. Rule 5 – Comprehensive Data Sublanguage Rule

The system must support at least one relational language (such as SQL) for data definition, manipulation, integrity constraints, and authorization.

3NF Connection: A normalized schema supports relational operations—joins, projections, and selections—without structural ambiguity. This makes it easier for SQL and other relational languages to enforce constraints consistently.

4. Rule 6 – View Updating Rule

All theoretically updatable views must be updatable by the system.

3NF Connection: 3NF removes derived or redundant attributes from base tables, making the resulting schema simpler. Consequently, views created from base tables are easier to maintain and update since each value is derived from a single logical source.

Indirectly Related Rules

5. Rule 9 – Logical Data Independence

Application programs and user views should not be affected by changes in the logical structure of the database.

3NF Connection: Because 3NF organizes data around primary keys and eliminates transitive dependencies, schema changes—like adding or modifying attributes—rarely impact existing tables or queries. This strengthens logical data independence.

6. Rule 10 – Integrity Independence

Integrity constraints must be stored in the database catalog and not embedded in application code.

3NF Connection: 3NF encourages data validation through schema-level constraints like PRIMARY KEY, FOREIGN KEY, and UNIQUE. By defining relationships at the database level, integrity enforcement becomes independent of external programs.

Rules Outside 3NF’s Scope

While 3NF contributes significantly to logical clarity, it does not directly address several of Codd’s rules that pertain to system functionality or physical data behavior. These include:

Rule 3 – Systematic Treatment of Nulls
Rule 4 – Active Online Catalog
Rule 7 – High-Level Insert, Update, Delete
Rule 8 – Physical Data Independence
Rule 11 – Distribution Independence
Rule 12 – Non-Subversion Rule

Summary Table: Relationship Between 3NF and Codd’s Rules

Codd Rule	3NF Alignment	Reason
Rule 1 – Information Rule	✅ Strongly aligned	All data stored logically in table form
Rule 2 – Guaranteed Access Rule	✅ Supports	Ensures single logical access path via primary key
Rule 5 – Data Sublanguage Rule	✅ Enables	Clean schema design supports relational language operations
Rule 6 – View Updating Rule	✅ Facilitates	Normalized structure supports updatable views
Rule 9 – Logical Data Independence	✅ Aids	Schema flexibility minimizes impact of design changes
Rule 10 – Integrity Independence	✅ Complements	Constraints enforced within schema instead of applications

Codd’s Normalization Slogan

To remember the first three normal forms, Codd offered a memorable slogan:

“The key, the whole key, and nothing but the key, so help me Codd.”

This slogan summarizes the essence of normalization:

The key: Eliminate repeating groups so that every table has a clear primary key (1NF).
The whole key: Ensure all attributes depend on the entire primary key, not just a part (2NF).
And nothing but the key: Remove transitive dependencies so non-key attributes depend only on the key (3NF).
So help me, Codd: A nod to E. F. Codd, the originator of relational theory.

This mnemonic mirrors the U.S. courtroom oath, “to tell the truth, the whole truth, and nothing but the truth,” emphasizing the logical rigor expected of relational database design.

DeNormalization Theory - Exercise

Before you move to the next lesson, click the Exercise link below to reinforce your understanding of normalization rules.
DeNormalization Theory - Exercise