<?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>