diff --git a/xml/rule.rng b/xml/rule.rng
index 2ed9a94543..2a71432861 100644
--- a/xml/rule.rng
+++ b/xml/rule.rng
@@ -1,123 +1,125 @@
 <?xml version="1.0" encoding="utf-8"?>
 <grammar xmlns="http://relaxng.org/ns/structure/1.0" 
-	 xmlns:a="http://relaxng.org/ns/compatibility/annotations/1.0"
+	 xmlns:ann="http://relaxng.org/ns/compatibility/annotations/1.0"
          datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
   <start>
       <ref name="element-rule"/>
   </start>
 
   <define name="element-rule">
     <element name="rule">
       <attribute name="id"><data type="ID"/></attribute>
       <choice>
 	<externalRef href="score.rng"/>
 	<attribute name="score_attribute"><data type="IDREF"/></attribute>
       </choice>
-      <attribute name="boolean-op">
-	<choice>
-	  <value>or</value>
-	  <value>and</value>
-	</choice>
-      </attribute>
+      <optional>
+	<attribute name="boolean-op">
+	  <choice>
+	    <value>or</value>
+	    <value>and</value>
+	  </choice>
+	</attribute>
+      </optional>
       <optional>
 	<attribute name="role"><text/></attribute>
       </optional>
       <oneOrMore>
 	<choice>
           <element name="expression">
 	    <attribute name="id"><data type="ID"/></attribute>
 	    <attribute name="attribute"><text/></attribute>
 	    <attribute name="operation">
 	      <choice>
 		<value>lt</value>
 		<value>gt</value>
 		<value>lte</value>
 		<value>gte</value>
 		<value>eq</value>
 		<value>ne</value>
 		<value>defined</value>
 		<value>not_defined</value>
 	      </choice>
 	    </attribute>
 	    <optional>
 	      <attribute name="value"><text/></attribute>
 	    </optional>
 	    <optional>
-	      <attribute name="type" a:defaultValue="string">
+	      <attribute name="type" ann:defaultValue="string">
 		<choice>
 		  <value>string</value>
 		  <value>number</value>
 		  <value>version</value>
 		</choice>
 	      </attribute>
 	    </optional>
 	  </element>
           <element name="date_expression">
 	    <attribute name="id"><data type="ID"/></attribute>
 	    <choice>
 	      <group>
 		<attribute name="operation">
 		  <choice>
 		    <value>in_range</value>
 		    <value>gt</value>
 		    <value>lt</value>
 		  </choice>
 		</attribute>
 		<attribute name="start"><data type="dateTime"/></attribute>
 		<optional>
 		  <attribute name="end"><data type="dateTime"/></attribute>
 		</optional>
 		<optional>
 		  <element name="duration">
 		    <ref name="date-common"/>
 		  </element> 
 		</optional>
 	      </group>
 	      <group>
 		<attribute name="operation"><value>date_spec</value></attribute>
 		<element name="date_spec">
 		  <ref name="date-common"/>
 		</element> 
 	      </group>
 	    </choice>
 	  </element> 
 	  <ref name="element-rule"/>
 	</choice>
       </oneOrMore>
     </element>
   </define>
 
   <define name="date-common">
     <attribute name="id"><data type="ID"/></attribute>
     <oneOrMore>
       <optional>
 	<attribute name="hours"><text/></attribute>
       </optional>
       <optional>
 	<attribute name="monthdays"><text/></attribute>
       </optional>
       <optional>
 	<attribute name="weekdays"><text/></attribute>
       </optional>
       <optional>
 	<attribute name="yearsdays"><text/></attribute>
       </optional>
       <optional>
 	<attribute name="months"><text/></attribute>
       </optional>
       <optional>
 	<attribute name="weeks"><text/></attribute>
       </optional>
       <optional>
 	<attribute name="years"><text/></attribute>
       </optional>
       <optional>
 	<attribute name="weekyears"><text/></attribute>
       </optional>
       <optional>
 	<attribute name="moon"><text/></attribute>
       </optional>
     </oneOrMore>
   </define>
 
 </grammar>