Constraint or Restriction on xsi:type

result.xml

<?xml version="1.0" encoding="UTF-8"?>
<Events xsi:noNamespaceSchemaLocation="file:///C:/StackOverflow.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
	<Event xsi:type="DerivedEvent1" Name="D1" Alpha="Content1"/>
	<Event xsi:type="DerivedEvent3" Name="D1" Gamma="Content3"/>
</Events>

StackOverflow.xsd

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
	<xs:complexType name="EventBase">
		<xs:annotation>
			<xs:documentation>***Abstract***</xs:documentation>
		</xs:annotation>
		<xs:attribute name="Name"/>
	</xs:complexType>
<xs:element name="Event" type="EventBase">
	<xs:annotation><xs:documentation>A generic event derived from abstract.</xs:documentation></xs:annotation>
</xs:element>
	<xs:complexType name="DerivedEvent1">
		<xs:complexContent>
			<xs:extension base="EventBase">
				<xs:attribute name="Alpha" type="xs:string"/>
			</xs:extension>
		</xs:complexContent>
	</xs:complexType>
	<xs:complexType name="DerivedEvent2">
		<xs:complexContent>
			<xs:extension base="EventBase">
				<xs:attribute name="Beta"/>
			</xs:extension>
		</xs:complexContent>
	</xs:complexType>
	<xs:complexType name="DerivedEvent3">
		<xs:complexContent>
			<xs:extension base="EventBase">
				<xs:attribute name="Gamma"/>
			</xs:extension>
		</xs:complexContent>
	</xs:complexType>
<xs:complexType name="EventsCollectionType">
	<xs:annotation><xs:documentation>Holds derived events</xs:documentation></xs:annotation>
	<xs:sequence>
		<xs:element ref="Event" maxOccurs="unbounded"/>
	</xs:sequence>
</xs:complexType>
<xs:element name="Events"><xs:annotation><xs:documentation>Concrete holder of events.</xs:documentation></xs:annotation>
	<xs:complexType>
		<xs:sequence>
			<xs:element ref="Event" maxOccurs="unbounded"/>
		</xs:sequence>
	</xs:complexType>
</xs:element>
</xs:schema>