Functional dependency and normalization
I am trying to find a great resource to study for functional dependency and normalization.
Anyone have any idea where should I look to? I am having difficulty differentiating whether a FD is in 1NF, 2NF or 3NF?
I've been reading Wikipedia and used Google search to find good research, but can't find any that explains it in simple terms.
Maybe you all can share on how you learned FD's and normalization during your life as well.
Answer
A functional dependency defines a functional relationship between attributes. For example: PersonId functionally determines BirthDate (normally written as PersonId -> BirthDate). Another way of saying this is: There is exactly one Birth Date for any given instance of a person. Note that the converse may or may not be true. Many people may have been born on the same day. Given a BirthDate we may find many PersonId sharing that date.
Sets of functional dependencies may be used to synthesize relations (tables). The definition of the first 3 normal forms, including Boyce Codd Normal Form (BCNF) is stated in terms of how a given set of relations represent functional dependencies. Fourth and fifth normal forms involve Multi-Valued dependencies (another kettle of fish).
Here are a few free resources about Functional Dependencies, Normalization and database design. Be prepared to exercise your brain and math skills when studying this material.
The following are "slide shows" from various academic sites...
- Functional Dependencies
- Functional Dependencies and Normalization for Relational Databases
- The Relational Data Model: Functional-Dependency Theory
The following are academic papers. Heavier reading but well worth the effort.
- The Application of Functional Dependency Theory to Relational Databases
- A Simple Guide to Five Normal Forms in Relational Database
- Simple Conditions for Guaranteeing Higher Normal Forms in Relational Databases
If you are seriously interested in this subject I suggest you put out the cash for a good book on the subject of Relational Database Design. For example: An Introduction to Database Systems by C.J. Date