Glossary

Natural Key - A natural key is a key that has meaning. An employee's social security number might be used to uniquely identify employees in an HR system (I would NOT recommend this but I have seen it). That would be a natural key.

NULL - an unknown value is said to be a NULL value. An empty string has a known value (it is empty), so it is not a NULL string. Unfortuanately, Oracle treats an empty string as if it is NULL. In programming, a NULL is never equal to anything, including NULL. IF NULL == (x) is never true no matter what the value of (x).