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 a 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.
1) This rule is at the heart of any relational database design.
2) Being able to find a datum is at the heart of 2NF. Relations in 1NF must have a primary key, though the relation can contain columns that are not functionally determined by the relation's primary key field
3)Deleting a record about an item should not also delete information about the company that makes it.
4)Maintaining referential integrity is an absolute requirement for a relational database. Putting all of database's tables in 3NF, complete with links between tables based on common fields, allows the RDBMS to check each table's contents.
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.
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.