--- a/xml/schema/extensions/prov-dictionary.xsd	Wed Jan 30 15:48:17 2013 -0700
+++ b/xml/schema/extensions/prov-dictionary.xsd	Wed Jan 30 16:23:59 2013 -0700
@@ -14,6 +14,16 @@
 	</xs:complexType>
 	
 	<xs:element name="dictionary" type="prov:Dictionary" substitutionGroup="prov:abstractElement" />
+	
+	<!-- Empty Dictionary -->
+	<xs:complexType name="EmptyDictionary">
+		<xs:complexContent>
+			<xs:extension base="prov:Dictionary">
+			</xs:extension>
+		</xs:complexContent>
+	</xs:complexType>
+	
+	<xs:element name="emptyDictionary" type="prov:EmptyDictionary" substitutionGroup="prov:abstractElement" />
 		
 	<!-- Key-Value Pair -->
 	<xs:complexType name="KeyValuePair">
@@ -23,6 +33,7 @@
         </xs:sequence>
 	</xs:complexType>
 	
+	<!-- do we need to have this use the substitutionGroup? -->
 	<xs:element name="keyValuePair" type="prov:KeyValuePair" substitutionGroup="prov:abstractElement"/>
 
 	<!-- Dictionary Membership -->