File: Data.xml
<?xml version="1.0"?>
<Course xmlns="http://www.wbex.ru"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation=
"http://www.wbex.ru
Schema.xsd">
<Books>
<Book>
<ISBN>1-111-11111-1</ISBN>
</Book>
<Book>
<ISBN>2-222-22222-2</ISBN>
</Book>
</Books>
<GuestAuthors>
<Author>
<BookForSigning>
<ISBN>2-222-22222-2</ISBN>
</BookForSigning>
</Author>
</GuestAuthors>
</Course>
File: Schema.xsd
<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.wbex.ru"
xmlns="http://www.wbex.ru"
xmlns:lib="http://www.wbex.ru"
elementFormDefault="qualified">
<xsd:element name="Book">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="ISBN" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="GuestAuthors">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="Author" minOccurs="0" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="BookForSigning" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="ISBN" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="Course">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="Books">
<xsd:complexType>
<xsd:sequence>
<xsd:element ref="Book" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element ref="GuestAuthors"/>
</xsd:sequence>
</xsd:complexType>
<xsd:key name="PK">
<xsd:selector xpath="lib:Books/lib:Book"/>
<xsd:field xpath="lib:ISBN"/>
</xsd:key>
<xsd:keyref name="isbnRef" refer="PK">
<xsd:selector xpath="lib:GuestAuthors/lib:Author/lib:BookForSigning"/>
<xsd:field xpath="lib:ISBN"/>
</xsd:keyref>
</xsd:element>
</xsd:schema>