embedding xml schema in an instance doc

[<peej@mindspring.com>]

Hi,

I'm attempteng to embed XML Schema elements within an instance document and running into trouble when Xerces attempts to validate, although XML Spy has no problem.  What I'd like to be able to do is put a "fragment" of XML Schema within an instance doc...like so:

...
<structure>
 <xsd:element name="record">
  <xsd:complexType>
   <xsd:sequence>
    <xsd:element ref="darwin:DateLastModified" /> 
    <xsd:element ref="darwin:InstitutionCode" /> 
    <xsd:element ref="darwin:CollectionCode" /> 
    <xsd:element ref="darwin:CatalogNumber" /> 
    <xsd:element ref="darwin:ScientificName" /> 
    <xsd:element ref="darwin:Genus" /> 
    <xsd:element ref="darwin:Species" /> 
   </xsd:sequence>
  </xsd:complexType>
 </xsd:element>
</structure>
...

I've tried a variety of things involving namespace declarations and namespace locations.  I'm wondering if I should even be able to do this.  Does an xml schema doc exist specifying XML Schema and if it does, should I not just be able to reference it from an instance as if it were any other schema document, via its namespace?

Any help would be appreciated!  Thanks in advance.

P.J.