hello

My book claims there are two kinds of relationships:
Two way connection and one way connection, but it doesn't go into any
more details.


Anyways, here are the graphical representations that my book uses for
displaying two way and one way relationships:

<<---------->> //this is two way many-to-many connection
<------------>> // this is two way one-to-many connection
-------------->> // this is one way one-to-many connection


At first I thought that one way connection would be between primary
key in a row and all other non-key attributes in that row. But that
doesn't make much sense since with SELECT statements ( in the WHERE
clause ) we can also use non-key attributes?! Can you help me a bit?


thank you