XSD validation, ambiguous root XML instance element

Hi all,
   Please look at following XSD validation use case, and my doubts
mentioned after that.

My XML instance document is following (that I wish to validate with XSD),

x.xml

<?xml version="1.0"?>
<X>
  <a>
    <p/>
  </a>
  <a>
    <q/>
  </a>
</X>

I'm validating the above cited XML instance document, with following XSD
document,

x.xsd

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

     <xs:include schemaLocation="x1.xsd"/>

     <xs:element name="X">
       <xs:complexType>
         <xs:sequence>
           <xs:element name="a" maxOccurs="unbounded">
              <xs:complexType>
                 <xs:sequence>
                    <xs:any/>
                 </xs:sequence>
              </xs:complexType>
           </xs:element>
         </xs:sequence>
       </xs:complexType>
     </xs:element>

</xs:schema>

Following is XSD document x1.xsd, that's included by above cited XSD
document,

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

   <xs:element name="p"/>

   <xs:element name="q"/>
</xs:schema>

When I do an XSD validation as stated above, the XML validation outcome is
reported as valid. This is ok with me.

Below are my doubts and concerns,

Due to an xs:include that I'm using, within the XSD document x.xsd, the
valid XML instance root elements can be X, p or q. But, I wish that, the
XML schema for my example above, should prohibit the XML instances root
elements p or q. I wish that, only an XML instance element X should be a
valid XML instance root. Is this achievable, with the current XSD 1.0 or
1.1 languages? If not, I'd like to suggest following changes to my XSD
document x.xsd,

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

     <xs:include schemaLocation="x1.xsd"/>

     <xs:root>
        <xs:assert test="not(self::p | self::q)"/>
     </xs:root>

     <xs:element name="X">
       <xs:complexType>
         <xs:sequence>
           <xs:element name="a" maxOccurs="unbounded">
              <xs:complexType>
                 <xs:sequence>
                    <xs:any/>
                 </xs:sequence>
              </xs:complexType>
           </xs:element>
         </xs:sequence>
       </xs:complexType>
     </xs:element>

</xs:schema>

i.e, I wish the following change to XSD language,
We should be able to specify an optional xs:root element as child of
xs:schema element, that can mention XML schema validation constraints for
the XML instance root element. With the above XSD document example, xs:root
element specifies that, XML elements p and q cannot be the root XML
elements of the XML document that's validated.

Any thoughts please?



-- 
Regards,
Mukul Gandhi