I have provided an example database that has two tables: a "parent" table and a "child" table. These two tables are connected via a foreign key relationship. Foreign keys are commonly used to reduce data redundancy. One of the maxims of computer science is: never store the same item in more than one place. (When you violate this rule, then, it's exremely likely that copies will diverge and chaos will reign.) A foreign key, to those C programmers in the class, is similar to a pointer, or, to C++ programmers, is similar to a reference. Or to FORTRAN programmers a EQUIVALENCE statement.