A relational DBMS stores information in a set of "tables", each of
which has a unique identifier or "primary key". The tables are then
related to one another using "foreign keys". A foreign key is simply the
primary key in a different table. Diagrammatically, a foreign key is depicted as a line
with an arrow at one end.
In the example below, "Customer ID" is the primary key (PK) in one
table and the foreign key (FK) in another. The arrow represents a
one-to-many relationship between the two tables. The relationship indicates that one
customer can have one or more orders. A given order, however, can be
initiated by one and only one customer.
