<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
   <xsd:element name= "contact" type="ContactType"/>
   <xsd:complexType name="ContactType">
      <xsd:choice minOccurs="2" maxOccurs="2">
         <xsd:element name="customer" type="xsd:string" />
         <xsd:element name="comment" type="xsd:string"  minOccurs="0"/>
      </xsd:choice>
   </xsd:complexType>
</xsd:schema>