Achieving Third Normal Form and Its Compliance with Codd's 12 Criteria

Achieving Third Normal Form (3NF) aligns with several of Codd's 12 Rules for a relational database system. While 3NF is a data modeling and normalization principle, and Codd’s 12 rules are system-level principles, there is meaningful conceptual overlap. Here's how achieving 3NF supports or embodies specific Codd rules:

1. 🔹 Rule 1: Information Rule
   • All information in a relational database is represented explicitly at the logical level and in exactly one way—by values in tables.
   • 3NF Benefit: By removing transitive dependencies and ensuring that each non-key attribute depends only on the primary key, data is stored in its simplest and most logical form using relational tables only.
2. 🔹 Rule 2: Guaranteed Access Rule
   • Each data item must be logically accessible by specifying the table name, primary key, and column name.
   • 3NF Benefit: 3NF enforces atomic and non-redundant data storage, which ensures clarity and unique access paths to each data item. You avoid having multiple paths to the same data via transitive dependencies.
3. 🔹 Rule 5: Comprehensive Data Sublanguage Rule
   • The system must support at least one relational language with linear syntax and support for data definition, manipulation, integrity constraints, and authorization.
   • 3NF Benefit: Proper normalization like 3NF makes the structure more amenable to being fully operated on by a relational language (e.g., SQL), especially when enforcing integrity constraints like foreign keys.
4. 🔹 Rule 6: View Updating Rule
   • All theoretically updatable views must be updatable by the system.
   • 3NF Benefit: A normalized design avoids unnecessary derived or computed fields in base tables, increasing the likelihood that views built upon them are updatable, since they map directly to base rows.

1. 🔹 Rule 9: Logical Data Independence
   
   • Application programs and user views are unaffected by changes in the logical structure of the database.
   • 3NF Benefit: By decoupling transitive dependencies, structural changes (e.g., adding new attributes to related entities) often don't impact existing tables, increasing data independence.
2. 🔹 Rule 10: Integrity Independence
   • Integrity constraints must be stored in the catalog, not in application programs.
   • 3NF Benefit: 3NF explicitly separates data structure from data logic, allowing integrity constraints (like foreign keys or uniqueness) to be defined at the schema level—not buried in application code.

Some Codd rules concern system behavior or capabilities (like transaction processing, rule 4; security, rule 11) rather than schema design. 3NF alone doesn’t guarantee adherence to:

• Rule 3: Systematic treatment of nulls
• Rule 4: Dynamic 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

Codd Rule	3NF Relevance	Reason
Rule 1	✅ Strongly aligned	Logical storage of data
Rule 2	✅ Supports	Unambiguous data access
Rule 5	✅ Enables	Clean structure supports query languages
Rule 6	✅ Facilitates	Views more likely to be updatable
Rule 9	✅ Aids	Logical changes don’t disrupt the schema
Rule 10	✅ Complements	Constraints can be enforced in schema

Conclusion: Achieving Third Normal Form directly supports Codd's vision of data independence, integrity, and logical clarity, which are embedded in several of his 12 rules. While 3NF is not a guarantee of full relational compliance, it is a foundational prerequisite for building relational systems that do.

To help remember the requirements for the first three normal forms, use this slogan:

• Codd Slogan for Normalization:
  

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

  
  
  1. “The key”: Tables may not contain repeating groups, which prevent a table from having a primary key. (1NF)
  2. “The whole key”: Every attribute must be functionally dependent on the entire primary key. (2NF)
  3. “And nothing but the key”: There may not be any transitive dependencies, which involve a non-key field. (3NF)
  4. “So help me, Codd”: The theorist who gave us these rules.

The slogan is based on the oath witnesses take in courts in the United States, which requires them to

tell "the truth, the whole truth, and nothing but the truth, so help me God."

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