Schema Help

Hello All,

In the instance xml file, if I would like to allow different xsi-type and 
just free text like below,

<gemq:priceCode 
xsi:type="gemq:URI">http://www.purl.org/gem/instance/GEMpriceCode/free</gemq:priceCode>
<gemq:priceCode xsi:type="gemq:GEMPriceCode">Free</gemq:priceCode>
<gemq:priceCode>free</gemq:priceCode>

How could I need to change following gemq xml schema?

<xs:element name="priceCode"/>

<xs:simpleType name="URI">
    <xs:restriction base="xs:anyURI"/>
</xs:simpleType>
<xs:element name="GEMPriceCode">
   <xs:simpleType>
       <xs:restriction base="xs:string">
           <xs:enumeration value="Free Based"/>
           <xs:enumeration value="Free"/>
           <xs:enumeration value="Partially Free"/>
      </xs:restriction>
  </xs:simpleType>
</xs:element>

I treid to do in multiple ways, it keeps generating validation errors.

Could you do me a big favor?

Thanks a lot,

Best regards,
Oknam