IF-ELSE in XML Schema

hi,
Is it possible to have IF-ELSE functionality in XML SChema
In my SCHEMA I have to select a Enumeration based on the values from 
another enumeration

    <simpleType name="Attributes">
     <restriction base="string">
      <enumeration value="Flight Number"/>
      <enumeration value="Class"/>
      <enumeration value="Fare"/>
      <enumeration value="Equipment"/>
      <enumeration value="Origin"/>
      <enumeration vlue="Destination"/>
      <enumeration value="Departure Date"/>
      <enumeration value="Arrival Date"/>
      <enumeration value="Record Locator"/>
      <enumeration value="Reservation Number"/>
       </restriction>
       </simpleType>

    <complexType name="AttrVal">
           <sequence>
      <element name="attrName" type="tns:Attributes">
      </element>
      <element name="valueText" type="string" minOccurs="0">
      </element>
        </sequence>
      </complexType>

In AttrVal schema I want ' valueText ' to be an Enumeration

like

if(attrName=="Flight Number") then valueText="values from other enum"

Thanx in advance
ankit