<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:opf="http://www.idpf.org/2007/opf"
           xmlns:dc="http://purl.org/dc/elements/1.1/"
           xmlns:xml="http://www.w3.org/XML/1998/namespace"
           targetNamespace="http://www.idpf.org/2007/opf"
           elementFormDefault="qualified"
           attributeFormDefault="unqualified">

    <xs:annotation>
        <xs:documentation>Schema for OPF 3.0 (Open Packaging Format)</xs:documentation>
    </xs:annotation>

    <xs:import namespace="http://purl.org/dc/elements/1.1/" schemaLocation="dc.txt"/>
    <xs:import namespace="http://www.w3.org/XML/1998/namespace" schemaLocation="xml.txt"/>

    <!-- Define custom yes/no type -->
    <xs:simpleType name="yes_or_no">
        <xs:restriction base="xs:string">
            <xs:enumeration value="yes"/>
            <xs:enumeration value="no"/>
        </xs:restriction>
    </xs:simpleType>

    <!-- Package -->
    <xs:element name="package">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="opf:metadata"/>
                <xs:element ref="opf:manifest"/>
                <xs:element ref="opf:spine"/>
                <xs:element ref="opf:guide" minOccurs="0"/>
                <xs:element ref="opf:bindings" minOccurs="0"/>
                <xs:element ref="opf:collection" minOccurs="0" maxOccurs="unbounded"/>
            </xs:sequence>
            <xs:attribute name="version" type="xs:string" use="required" fixed="3.0"/>
            <xs:attribute name="unique-identifier" type="xs:string" use="required"/>
            <xs:attribute name="prefix" type="xs:string"/>
            <xs:attribute ref="xml:lang"/>
            <xs:attribute name="dir">
                <xs:simpleType>
                    <xs:restriction base="xs:string">
                        <xs:enumeration value="ltr"/>
                        <xs:enumeration value="rtl"/>
                    </xs:restriction>
                </xs:simpleType>
            </xs:attribute>
            <xs:attribute name="id" type="xs:ID"/>
        </xs:complexType>
    </xs:element>

    <!-- Metadata -->
    <xs:element name="metadata">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="dc:identifier" maxOccurs="unbounded"/>
                <xs:element ref="dc:title" maxOccurs="unbounded"/>
                <xs:element ref="dc:language" maxOccurs="unbounded"/>
                <xs:element ref="dc:creator" minOccurs="0" maxOccurs="unbounded"/>
                <xs:element ref="dc:contributor" minOccurs="0" maxOccurs="unbounded"/>
                <xs:element ref="dc:date" minOccurs="0" maxOccurs="unbounded"/>
                <xs:element ref="dc:subject" minOccurs="0" maxOccurs="unbounded"/>
                <xs:element ref="dc:description" minOccurs="0" maxOccurs="unbounded"/>
                <xs:element ref="dc:publisher" minOccurs="0" maxOccurs="unbounded"/>
                <xs:element ref="dc:type" minOccurs="0" maxOccurs="unbounded"/>
                <xs:element ref="dc:format" minOccurs="0" maxOccurs="unbounded"/>
                <xs:element ref="dc:source" minOccurs="0" maxOccurs="unbounded"/>
                <xs:element ref="dc:relation" minOccurs="0" maxOccurs="unbounded"/>
                <xs:element ref="dc:coverage" minOccurs="0" maxOccurs="unbounded"/>
                <xs:element ref="dc:rights" minOccurs="0" maxOccurs="unbounded"/>
                <xs:element name="meta" minOccurs="0" maxOccurs="unbounded">
                    <xs:complexType>
                        <xs:simpleContent>
                            <xs:extension base="xs:string">
                                <xs:attribute name="property" type="xs:string" use="required"/>
                                <xs:attribute name="scheme" type="xs:string"/>
                                <xs:attribute name="id" type="xs:ID"/>
                                <xs:attribute ref="xml:lang"/>
                                <xs:attribute name="dir">
                                    <xs:simpleType>
                                        <xs:restriction base="xs:token">
                                            <xs:enumeration value="ltr"/>
                                            <xs:enumeration value="rtl"/>
                                        </xs:restriction>
                                    </xs:simpleType>
                                </xs:attribute>
                            </xs:extension>
                        </xs:simpleContent>
                    </xs:complexType>
                </xs:element>
                <xs:element name="link" minOccurs="0" maxOccurs="unbounded">
                    <xs:complexType>
                        <xs:attribute name="href" type="xs:anyURI" use="required"/>
                        <xs:attribute name="rel" type="xs:string" use="required"/>
                        <xs:attribute name="id" type="xs:ID"/>
                        <xs:attribute name="media-type" type="xs:string"/>
                    </xs:complexType>
                </xs:element>
            </xs:sequence>
        </xs:complexType>
    </xs:element>

    <!-- Manifest -->
    <xs:element name="manifest">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="opf:item" maxOccurs="unbounded"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>

    <xs:element name="item">
        <xs:complexType>
            <xs:attribute name="id" type="xs:ID" use="required"/>
            <xs:attribute name="href" type="xs:anyURI" use="required"/>
            <xs:attribute name="media-type" type="xs:string" use="required"/>
            <xs:attribute name="fallback" type="xs:IDREF"/>
            <xs:attribute name="properties" type="xs:string"/>
            <xs:attribute name="media-overlay" type="xs:IDREF"/>
        </xs:complexType>
    </xs:element>

    <!-- Spine -->
    <xs:element name="spine">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="opf:itemref" maxOccurs="unbounded"/>
            </xs:sequence>
            <xs:attribute name="id" type="xs:ID"/>
            <xs:attribute name="page-progression-direction">
                <xs:simpleType>
                    <xs:restriction base="xs:token">
                        <xs:enumeration value="ltr"/>
                        <xs:enumeration value="rtl"/>
                        <xs:enumeration value="default"/>
                    </xs:restriction>
                </xs:simpleType>
            </xs:attribute>
            <xs:attribute name="toc" type="xs:IDREF"/>
        </xs:complexType>
    </xs:element>

    <xs:element name="itemref">
        <xs:complexType>
            <xs:attribute name="idref" type="xs:IDREF" use="required"/>
            <xs:attribute name="linear" type="yes_or_no" default="yes"/>
            <xs:attribute name="id" type="xs:ID"/>
            <xs:attribute name="properties" type="xs:string"/>
        </xs:complexType>
    </xs:element>

    <!-- Guide -->
    <xs:element name="guide">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="opf:reference" maxOccurs="unbounded"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>

    <xs:element name="reference">
        <xs:complexType>
            <xs:attribute name="type" use="required"/>
            <xs:attribute name="title" type="xs:string"/>
            <xs:attribute name="href" type="xs:anyURI" use="required"/>
        </xs:complexType>
    </xs:element>

    <!-- Bindings -->
    <xs:element name="bindings">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="opf:mediaType" maxOccurs="unbounded"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>

    <xs:element name="mediaType">
        <xs:complexType>
            <xs:attribute name="media-type" type="xs:string" use="required"/>
            <xs:attribute name="handler" type="xs:IDREF" use="required"/>
        </xs:complexType>
    </xs:element>

    <!-- Collection -->
    <xs:element name="collection">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="opf:metadata" minOccurs="0"/>
                <xs:choice maxOccurs="unbounded">
                    <xs:element ref="opf:collection"/>
                    <xs:element name="link">
                        <xs:complexType>
                            <xs:attribute name="href" type="xs:anyURI" use="required"/>
                            <xs:attribute name="rel" type="xs:string"/>
                            <xs:attribute name="id" type="xs:ID"/>
                            <xs:attribute name="media-type" type="xs:string"/>
                        </xs:complexType>
                    </xs:element>
                </xs:choice>
            </xs:sequence>
            <xs:attribute name="role" type="xs:string" use="required"/>
            <xs:attribute name="id" type="xs:ID"/>
            <xs:attribute ref="xml:lang"/>
            <xs:attribute name="dir">
                <xs:simpleType>
                    <xs:restriction base="xs:token">
                        <xs:enumeration value="ltr"/>
                        <xs:enumeration value="rtl"/>
                    </xs:restriction>
                </xs:simpleType>
            </xs:attribute>
        </xs:complexType>
    </xs:element>

</xs:schema>