diff --git a/resources/schema/lexonomy.xsd b/resources/schema/lexonomy.xsd
index 4ce9f3e..0b6c038 100644
--- a/resources/schema/lexonomy.xsd
+++ b/resources/schema/lexonomy.xsd
@@ -85,7 +85,7 @@
         <xsd:complexType>
           <xsd:simpleContent>
             <xsd:extension base="xsd:string">
-              <xsd:attribute name="lexical_unit_id" type="xsd:int" use="required"/>
+              <xsd:attribute name="lexical_unit_id" type="xsd:int"/>
             </xsd:extension>
           </xsd:simpleContent>
         </xsd:complexType>
@@ -99,7 +99,7 @@
         <xsd:complexType>
           <xsd:simpleContent>
             <xsd:extension base="xsd:string">
-              <xsd:attribute name="type" type="xsd:string" use="required"/>
+              <xsd:attribute name="type" type="xsd:string"/>
             </xsd:extension>
           </xsd:simpleContent>
         </xsd:complexType>
@@ -125,6 +125,7 @@
     <xsd:simpleContent>
       <xsd:extension base="xsd:string">
         <xsd:attribute name="targetLang" type="xsd:string" use="required"/>
+        <xsd:attribute name="source" type="xsd:string"/>
       </xsd:extension>
     </xsd:simpleContent>
   </xsd:complexType>