
<p>We can illustrate this with a somewhat useless (but simple) example, which
replaces the standard generators for item number and supplier name

<pre>
(select (@Item)
   ((nr +Item @Nr) (nm +CuSu @Sup (sup +Item)))
   ...
</pre>

<p>with the equivalent form

<pre>
(select (@Item)
   ((@A (@Nr) ((db nr +Item @Nr @A)))
      (@B (@Sup) ((db nm +CuSu @Sup @B)) (sup +Item)) )
</pre>

<p>That is, a query with the <code><a href="refD.html#db/3">db/3</a></code> tree
iteration predicate is used to generate approp