--- a/model/prov-constraints.html	Thu Jul 19 10:12:29 2012 +0100
+++ b/model/prov-constraints.html	Thu Jul 19 10:22:00 2012 +0100
@@ -1632,6 +1632,27 @@
 </ol>
 </p>   </div>
 
+   <hr />
+   <p id='key_relation2_text'> Furthermore,  identifiers
+   of relationships in PROV uniquely identify a relation (except for wasInfluencedBy), through
+  the following key constraints:
+  </p>
+  <div class='constraint' id='key-relation2'>
+    <p>The <span
+  class="name">id</span> field is a KEY for <span
+  class="name">r(id;a_1,...,a_n)</span>
+for any relation type r in { 
+<span class="name">used</span>,
+<span class="name">wasGeneratedBy</span>,
+<span class="name">wasInfluencedBy</span>,
+<span class="name">wasStartedBy</span>,
+<span class="name">wasEndedBy</span>,
+<span class="name">wasInformedBy</span>,
+<span class="name">wasAttributedTo</span>,
+<span class="name">wasAssociatedWith</span>,
+<span class="name">actedOnBehalfOf</span>}
+</p>   </div>
+
 
 <hr>