--- a/model/working-copy/towards-wd4.html	Fri Feb 03 21:39:10 2012 +0100
+++ b/model/working-copy/towards-wd4.html	Fri Feb 03 21:49:01 2012 +0100
@@ -236,7 +236,7 @@
 <p><dfn id="concept-generation">Generation</dfn> is the completed production of a new entity by activity.
  This entity become available for usage after this generation. This entity did not exist before generation. </p>
 
-<p><dfn id="concept-usage">Usage</dfn> is an activity beginning to consume an entity.
+<p><dfn id="concept-usage">Usage</dfn> is the beginning on  an entity being consumed by an activity.
 Before usage, the activity had not begun to consume or use to this entity (and could not have been affected by the entity).</p>
 </p>
 
@@ -251,6 +251,22 @@
 the mix), or leave it as such, ready for further uses (e.g. a file on a file system can be read indefinitely).</p>
 </div>
 
+<p>Activities are consumers of entities and producers of entities. In some case, the consumption of entity influences the creation of another in some way. This notion is captured by derivations, defined as follows.</p>
+
+<p><dfn id="concept-derivation">Derivation</dfn> is the fact that some entity is transformed from, created from, or affected by another entity in the world.  </p>
+<!-- doesn't seem right to say fact, should I use influence? -->
+
+
+<p>In PROV-DM, a <dfn id="dfn-Derivation">derivation record</dfn> is a representation that some entity is transformed from, created from, or affected by another entity in the world.  </p>
+
+
+<p>Examples of derivation include the transformation of a canvas into a painting, the transportation of a person from London to New York, the transformation of a relational table into a
+linked data set, and the melting of ice into water.</p>
+
+
+<p>Examples of derivation include the transformation of a canvas into a painting, the transportation of a person from London to New York, the transformation of a relational table into a
+linked data set, and the melting of ice into water.</p>
+
 
 </section>
 </section>