When you call one or more columns as your primary key then this is what is called a composite primary key. Some of even the talented computer programmers have never used them and some may have not even know that they exist. Yet when making a solid data model composite primary keys are a major factor. It is important for many to understand that composite primary keys are out there available to be
. used. To learn more on composite primary keys and how to use them visit http://searchoracle.techtarget.com/expert/KnowledgebaseAnswer/0,289625,sid41_gci1072544,00.html.