<xs:schema xmlns:xs=“www.w3.org/2001/XMLSchema”>
<xs:element name="family" type="family_type"> <xs:key name="sibling_key"> <xs:selector xpath="siblings/sibling"/> <xs:field xpath="@name"/> </xs:key> <xs:keyref name="sibling_key_ref" refer="sibling_key"> <xs:selector xpath="sisters/sister"/> <xs:field xpath="@name"/> </xs:keyref> </xs:element> <xs:complexType name="family_type"> <xs:sequence> <xs:element name="siblings" type="siblings_type" /> <xs:element name="sisters" type="sisters_type" /> </xs:sequence> <xs:attribute name="name" type="xs:string"/> </xs:complexType> <xs:complexType name="siblings_type"> <xs:sequence> <xs:element name="sibling" type="sibling_type" minOccurs="0"
maxOccurs=“unbounded” />
</xs:sequence> </xs:complexType> <xs:complexType name="sisters_type"> <xs:sequence> <xs:element name="sister" type="sister_type" minOccurs="0"
maxOccurs=“unbounded” />
</xs:sequence> </xs:complexType> <xs:complexType name="sibling_type"> <xs:attribute name="name" type="xs:string"/> </xs:complexType> <xs:complexType name="sister_type"> <xs:attribute name="name" type="xs:string"/> </xs:complexType>
</xs:schema>