g predicate expressions.  The front end is concerned with providing an easy and expressive syntax.</p>
</dd>
<dt class="hdlist1">Graph</dt>
<dd>
<p>The graph component gathers all predicate expressions and merges common subexpression, forming a directed acyclic graph (DAG).  It then executes a variety of validation and transformations on the DAG.  Each input predicate expression corresponds to a <strong>root</strong> node in the DAG.</p>
</dd>
<dt class="hdlist1">Evaluation</dt>
<dd>
<p>At each transaction,