Third Normal Form   «Prev  Next»

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

Achieving Third Normal Form

Adheres to Codd's 12 Criteria for Normalization

E.F. Codd, the theoretician who laid the groundwork for relational databases, in an article published in the October 1985 edition of Computerworld, described 12 rules of fully relational database.
The theory went relatively unchallenged, but his comparisons of existing database systems ruffled feathers because, according to Codd's criteria, some were marketed as relational when they were not.
Most of Codd's 12 criteria establish rules for how the RDBMS handles things internally and only peripherally influence how users design databases to be managed by the RDBMS. Designing a database in third normal form makes it possible for the RDBMS to follow Codd's rules. There are four rules that stand out.

Four Important Rules

Slogan to Remember Codd's Criteria

If you are having trouble remembering which requirements go with which normal form, there is a slogan you can use to keep them in order.

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.

Codds Normalization Basis
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."

The next lesson discusses normalization beyond 3NF.

Normalization - Exercise

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