<xs:group name="ConceptRelationshipsGroup">
    <xs:annotation>
        <xs:documentation>A group of properites required to indicate relationships of the concept to other concepts</xs:documentation>
    </xs:annotation>
    <xs:sequence>
        <xs:choice minOccurs="0" maxOccurs="unbounded">
            <xs:element ref="sameAs" />
            <xs:element ref="broader" />
            <xs:element ref="narrower" />
            <xs:element ref="related" />
        </xs:choice>
    </xs:sequence>
</xs:group>