Schema Help

Hello.

I have two questions. It would be appreciated if you could give me some 
help.

1) How could I define type="xs:anyURI"
for identifier element below? it should be for only identifier, not 
sub-element such as gemq:sid, etc.

<xs:element name="identifier">
   <xs:complexType mixed="true">
             <xs:sequence>
	<xs:element ref="gemq:bibliographicCitation" minOccurs="0" 
maxOccurs="unbounded"/>
	<xs:element ref="gemq:publicID" minOccurs="0" maxOccurs="unbounded"/>
	<xs:element ref="gemq:sid"/>
	<!-- mandatory -->
	<xs:element ref="gemq:sdn"/>
	<!-- mandatory -->
	<xs:element ref="gemq:gemRecordID"/>
	<!-- mandatory -->
	</xs:sequence>
     </xs:complexType>

2) How could I allow to represent "<dc:description xml:lang='en'>" in a xml 
instance file in a schem below?

<xs:element name="description">
    <xs:complexType mixed="true">
	<xs:sequence>
	     <xs:element ref="dcterms:abstract" minOccurs="0" 
maxOccurs="unbounded"/>
	    <xs:element ref="dcterms:tableOfContents" minOccurs="0" 
maxOccurs="unbounded"/>
	</xs:sequence>
   </xs:complexType>
</xs:element>

Thanks a lot,

Best regards,
Oknam Park