diff --git a/xsd/vo-dml-v1.0.xsd b/xsd/vo-dml-v1.0.xsd
index 26ecfc4..f9f3182 100644
--- a/xsd/vo-dml-v1.0.xsd
+++ b/xsd/vo-dml-v1.0.xsd
@@ -498,29 +498,29 @@ TBD continue based on VO-DML specification document.
     </xsd:annotation>
     <xsd:complexContent>
       <xsd:extension base="Type">
-        <xsd:sequence>
-          <xsd:element name="attribute" type="Attribute" minOccurs="0" maxOccurs="unbounded">
+        <xsd:choice minOccurs="0" maxOccurs="unbounded">
+          <xsd:element name="attribute" type="Attribute" minOccurs="1" maxOccurs="1">
             <xsd:annotation>
               <xsd:documentation>
                 TODO
               </xsd:documentation>
             </xsd:annotation>
           </xsd:element>
-            <xsd:element name="composition" type="Composition" minOccurs="0" maxOccurs="unbounded">
+            <xsd:element name="composition" type="Composition" minOccurs="1" maxOccurs="1">
             <xsd:annotation>
               <xsd:documentation>
                 TODO
               </xsd:documentation>
             </xsd:annotation>
           </xsd:element>
-          <xsd:element name="reference" type="Reference" minOccurs="0" maxOccurs="unbounded">
+          <xsd:element name="reference" type="Reference" minOccurs="1" maxOccurs="1">
             <xsd:annotation>
               <xsd:documentation>
                 TODO
               </xsd:documentation>
             </xsd:annotation>
           </xsd:element>
-        </xsd:sequence>
+        </xsd:choice>
       </xsd:extension>
     </xsd:complexContent>
   </xsd:complexType>
@@ -556,22 +556,22 @@ TBD continue based on VO-DML specification document.
   <xsd:complexType name="DataType">
     <xsd:complexContent>
       <xsd:extension base="ValueType">
-        <xsd:sequence>
-          <xsd:element name="attribute" type="Attribute" minOccurs="0" maxOccurs="unbounded">
+        <xsd:choice minOccurs="0" maxOccurs="unbounded">
+          <xsd:element name="attribute" type="Attribute" minOccurs="1" maxOccurs="1">
             <xsd:annotation>
               <xsd:documentation>
                 TODO
               </xsd:documentation>
             </xsd:annotation>
           </xsd:element>
-          <xsd:element name="reference" type="Reference" minOccurs="0" maxOccurs="unbounded">
+          <xsd:element name="reference" type="Reference" minOccurs="1" maxOccurs="1">
             <xsd:annotation>
               <xsd:documentation>
                 TODO
               </xsd:documentation>
             </xsd:annotation>
           </xsd:element>
-        </xsd:sequence>
+        </xsd:choice>
       </xsd:extension>
     </xsd:complexContent>
   </xsd:complexType>