--- a/model/prov-dm.html	Mon May 28 15:05:24 2012 +0100
+++ b/model/prov-dm.html	Mon May 28 15:09:43 2012 +0100
@@ -1881,6 +1881,9 @@
 <li><span class='attribute' id="association.attributes">attributes</span>: an OPTIONAL set (<span class="name">attrs</span>) of attribute-value pairs representing additional information about this association of this activity with this agent.</li>
 </ul></div>
 
+<p>While each of <a href="#association.id"><span class='attribute'>id</span></a>, <a href="#association.agent"><span class='attribute'>agent</span></a>,  <a href="#association.plan"><span class='attribute'>plan</span></a>, and  <a href="#association.attributes"><span class='attribute'>attributes</span></a> is OPTIONAL, at least one of them MUST be present.</p>
+
+
 <div class="anexample" id="anexample-wasAssociatedWith">
 <p>In the following example, a designer agent and an operator agent are associated with an activity. The designer's goals are achieved by a workflow <span class="name">ex:wf</span>, described as an an entity of type <span class="name"><a>plan</a></span>.   </p>
 <pre class="codeexample">