title: Cardinality and foreign key relationship
body: <p>I am new to database design and am trying to understand the best practice for using foreign keys.  I know that when you have a 1:m relationship, we don't have to create a relation for the relationship; instead we could add a foreign key to the m-side of the relationship(which corresponds to the primary key on the 1-side) so as to preserve referential integrity.  My question however is:  Under what other circumstances could we do the same?  Can we do the same when we have a 0..1 to 1 or 1-1 relationship as well?  What is the best practice for this type of situation when referential integrity is as important as the computational cost?</p>