--Пример xml
<root>
	<Item User="Pupkin" Color="red" Is_Valid="true"/>
	<Item User="Ivanov"/>
</root>

--Схема для него
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
	<xs:element name="Item">
		<xs:complexType>
			<xs:attribute name="User" type="xs:string" use="required"/>
			<xs:attribute name="Color" type="xs:string" use="optional"/>
			<xs:attribute name="Is_Valid" type="xs:boolean" use="optional"/>
		</xs:complexType>
	</xs:element>
	<xs:element name="root">
		<xs:complexType>
			<xs:sequence>
				<xs:element ref="Item" maxOccurs="unbounded"/>
			</xs:sequence>
		</xs:complexType>
	</xs:element>
</xs:schema>