arted building a data model putting our
data into multiple linked tables, and linking the rows in those
tables using <b>keys</b>, we need to look at some terminology 
around keys. There are generally three kinds of keys used 
in a database model.
</font><ul><li><font color="black">A <b>logical key</b> is a key that the "real world" might use
to look up a row. In our example data model, the <tt>name</tt>
field is a logical key. It is the screen name for the user 
and we indeed look up a user's row several ti