XSD element substitution group example?
Use an element substitution group...
XSD
<?xml version="1.0" encoding="UTF-8"?><xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="Sea"> <xs:complexType> <xs:sequence> <xs:element ref="FishSubGroup" minOccurs="0" maxOccurs="unbounded"/> </xs:sequence> <xs:attribute name="name" type="xs:string" use="optional"/> </xs:complexType> </xs:element> <xs:element name="FishSubGroup" abstract="true"/> <xs:element name="Tuna" type="FishType" substitutionGroup="FishSubGroup"/> <xs:element name="Carp" type="FishType" substitutionGroup="FishSubGroup"/> <xs:element name="Salmon" type="FishType" substitutionGroup="FishSubGroup"/> <xs:complexType name="FishType"> <xs:attribute name="name" type="xs:string"/> </xs:complexType></xs:schema>XML
<?xml version="1.0" encoding="UTF-8"?><Sea name="Atlantic Ocean"> <Tuna name="tuna1"/> <Carp name="carp1"/> <Carp name="carp2"/> <Tuna name="tuna2"/> <Salmon name="salmon1"/></Sea>