Recall that in PROLOG, queries can be thought of as specifying patterns in predicates and their conjunctions.
For example, "Find all the children of Mark", would translate into
<pre><B>
father(mark,X).
</b></pre>
As explained in class, you can think of <tt>father</tt> as the relation (predicate),
and the two fields to be the attributes (arguments), like so:
<pre><B>
--------------------------------------
|    person       |       child      |
--------------------------------------
|    Jones	  |	  King	     |
|    Jones	  |	  Smith      |
|    Smith        |	  Lew        |
|    Smith        |       Bandu      |
|    Smith        |       Davin      |
|    Mark         |       Higgins    |
|    Mark         | 	  Duke       |
|    Mark         |       Dan        |
|    Mark         |       Cherry     |
--------------------------------------
</B></pre>
so the above query would get you the solution {Higgins, Duke, Dan, Cherry}.
Alternatively, you can think of the above query as a single rule:
<pre><B>
q(X) :- father(mark,X).
q(X) ?
</B></pre>
wherein we compute the set of all children of Mark and form a new relation (q) with it (akin to a view in
RDBMS terms), and then we submit
a query for q. You might need to do this, if your queries get more complicated.</P>