Craig Nelson's List: Database Design

"unctional Dependency

Functional Dependencies A Functional Dependency describes a relationship between attributes in a single relation. An attribute is functionally dependant on another if we can use the value of one attribute to determine the value of another. "

"This tutorial briefly explains the concepts of referential integrity, and looks at how MySQL enforces them with its definition of foreign keys. You should be using a stable version of MySQL 4 to follow all the examples, although some examples may work with earlier versions running InnoDB tables.
What is referential integrity?

Simply put, referential integrity means that when a record in a table refers to a corresponding record in another table, that corresponding record will exist. Look at the following: "

"A feature provided by relational database management systems (RDBMS's) that prevents users or applications from entering inconsistent data. Most RDBMS's have various referential integrity rules that you can apply when you create a relationship between two tables. "

"Referential integrity is a property of data which, when satisfied, requires every value of one attribute (column) of a relation (table) to exist as a value of another attribute in a different (or the same) relation (table)."

"The concept of functional dependency (also known as normalization was introduced by professor Codd in 1970 when he defined the first three normal forms (first, second and third normal forms). Normalization is used to avoid or eliminate the three types of anomalies (insertion, deletion and update anomalies) which a database may suffer from"

n mathematics, a transitive dependency is a functional dependency which holds by virtue of transitivity. A transitive dependency can occur only in a relation that has three or more attributes. Let A, B, and C designate three distinct attributes (or distinct collections of attributes) in the relation. Suppose all three of the following conditions hold: