1<?xml version="1.0" encoding="utf-8"?>
2<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
3  <xs:element name="odd-page" type="xs:string"/>
4  <xs:element name="even-page" type="xs:string"/>
5  <xs:element name="book">
6    <xs:complexType>
7      <xs:sequence>
8        <xs:sequence minOccurs="0" maxOccurs="unbounded">
9          <xs:element ref="odd-page"/>
10          <xs:element ref="even-page"/>
11        </xs:sequence>
12        <xs:element ref="odd-page" minOccurs="0"/>
13      </xs:sequence>
14    </xs:complexType>
15  </xs:element>
16</xs:schema>
17