--- a/model/ProvenanceModel.html	Wed Sep 07 16:43:37 2011 +0100
+++ b/model/ProvenanceModel.html	Wed Sep 07 16:51:07 2011 +0100
@@ -528,6 +528,37 @@
 
 <div class='issue'>Conceptual model needs a high level overview <a href="http://www.w3.org/2011/prov/track/issues/86">ISSUE-86</a>.</div>
 
+   <section id="PIDM-expression"> 
+      
+<h3>PIDM Expression</h3>
+
+<div class='grammar'>
+<span class="nonterminal">expression</span>&nbsp;:=  
+<span class="nonterminal">node</span>   <!-- better name than node?? -->
+| <span class="nonterminal">relation</span> 
+| <span class="nonterminal">assertionBundle</span> 
+<br/>
+<!-- -->
+<span class="nonterminal">node</span>&nbsp;:=  
+<span class="nonterminal">entity</span> 
+|<span class="nonterminal">processExecution</span> 
+|<span class="nonterminal">agent</span> <br/>
+<!-- -->
+<span class="nonterminal">relation</span>&nbsp;:=  
+<span class="nonterminal">generation</span> 
+|<span class="nonterminal">use</span> 
+|<span class="nonterminal">derivation</span> 
+|<span class="nonterminal">control</span> 
+|<span class="nonterminal">complement</span> 
+|<span class="nonterminal">peOrdering</span> 
+|<span class="nonterminal">revision</span> 
+|<span class="nonterminal">participation</span> <br/>
+<!-- -->
+<span class="nonterminal">assertionBundles</span>&nbsp;:=  
+<span class="nonterminal">container</span> 
+|<span class="nonterminal">account</span> 
+</div>
+</section>
     
    <section id="expression-Entity">