<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
	
	<xsd:simpleType name="myDecimal">
		<xsd:restriction base="xsd:decimal">			
			<xsd:totalDigits value="18"/>			
		</xsd:restriction>
	</xsd:simpleType>

	<xsd:element name="foo">
		<xsd:complexType>
			<xsd:sequence>
				<xsd:element name="val" type="myDecimal" maxOccurs="unbounded"/>
				<xsd:element name="ref" type="myDecimal" minOccurs="0"/>
			</xsd:sequence>
		</xsd:complexType>

		<!--xsd:key name="myKey">
			<xsd:selector xpath="val"/>
			<xsd:field xpath="."/>
		</xsd:key>

		<xsd:keyref name="myKeyRef" refer="myKey">
			<xsd:selector xpath="ref"/>
			<xsd:field xpath="."/>
		</xsd:keyref-->
	</xsd:element>

</xsd:schema>