<?xml version=“1.0”?> <xsd:schema xmlns:xsd=“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>