<?xml version="1.0" encoding="utf-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           targetNamespace="http://www.w3.org/1999/xlink"
           xmlns:xlink="http://www.w3.org/1999/xlink">

  <xs:import namespace="http://www.w3.org/XML/1998/namespace"/>

  <xs:attribute name="type" type="xlink:typeType"/>

  <xs:simpleType name="typeType">
    <xs:restriction base="xs:token">
      <xs:enumeration value="simple"/>
      <xs:enumeration value="extended"/>
      <xs:enumeration value="title"/>
      <xs:enumeration value="resource"/>
      <xs:enumeration value="locator"/>
      <xs:enumeration value="arc"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:attribute name="href" type="xlink:hrefType"/>

  <xs:simpleType name="hrefType">
    <xs:restriction base="xs:anyURI"/>
  </xs:simpleType>

  <xs:attribute name="role" type="xlink:roleType"/>

  <xs:simpleType name="roleType">
    <xs:restriction base="xs:anyURI">
      <xs:minLength value="1"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:attribute name="arcrole" type="xlink:arcroleType"/>

  <xs:simpleType name="arcroleType">
    <xs:restriction base="xs:anyURI">
      <xs:minLength value="1"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:attribute name="title" type="xlink:titleAttrType"/>

  <xs:simpleType name="titleAttrType">
    <xs:restriction base="xs:string"/>
  </xs:simpleType>

  <xs:attribute name="show" type="xlink:showType"/>

  <xs:simpleType name="showType">
    <xs:restriction base="xs:token">
      <xs:enumeration value="new"/>
      <xs:enumeration value="replace"/>
      <xs:enumeration value="embed"/>
      <xs:enumeration value="other"/>
      <xs:enumeration value="none"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:attribute name="actuate" type="xlink:actuateType"/>

  <xs:simpleType name="actuateType">
    <xs:restriction base="xs:token">
      <xs:enumeration value="onLoad"/>
      <xs:enumeration value="onRequest"/>
      <xs:enumeration value="other"/>
      <xs:enumeration value="none"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:attribute name="label" type="xlink:labelType"/>

  <xs:simpleType name="labelType">
    <xs:restriction base="xs:NMTOKEN"/>
  </xs:simpleType>

  <xs:attribute name="from" type="xlink:fromType"/>

  <xs:simpleType name="fromType">
    <xs:restriction base="xs:NMTOKEN"/>
  </xs:simpleType>

  <xs:attribute name="to" type="xlink:toType"/>

  <xs:simpleType name="toType">
    <xs:restriction base="xs:NMTOKEN"/>
  </xs:simpleType>

  <xs:complexType mixed="true" name="simple">
    <xs:annotation>
      <xs:documentation>
        Intended for use as the type of user-declared elements to make them
        simple links.
      </xs:documentation>
    </xs:annotation>
    <xs:sequence>
      <xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
    </xs:sequence>
    <xs:attribute ref="xlink:type" fixed="simple"/>
    <xs:attribute ref="xlink:href"/>
    <xs:attribute ref="xlink:role"/>
    <xs:attribute ref="xlink:arcrole"/>
    <xs:attribute ref="xlink:title"/>
    <xs:attribute ref="xlink:show"/>
    <xs:attribute ref="xlink:actuate"/>
  </xs:complexType>

  <xs:complexType name="extended">
    <xs:annotation>
      <xs:documentation>
        Intended for use as the type of user-declared elements to make them
        extended links.
        Note that the elements referenced in the content model are all abstract.
        The intention is that by simply declaring elements with these as their
        substitutionGroup, all the right things will happen.
      </xs:documentation>
    </xs:annotation>
    <xs:choice minOccurs="0" maxOccurs="unbounded">
      <xs:element ref="xlink:title"/>
      <xs:element ref="xlink:resource"/>
      <xs:element ref="xlink:locator"/>
      <xs:element ref="xlink:arc"/>
    </xs:choice>
    <xs:attribute ref="xlink:type" fixed="extended"/>
    <xs:attribute ref="xlink:role"/>
    <xs:attribute ref="xlink:title"/>
  </xs:complexType>

  <xs:element name="title" type="xlink:titleEltType" abstract="true"/>

  <xs:complexType mixed="true" name="titleEltType">
    <xs:sequence>
      <xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
    </xs:sequence>
    <xs:attribute ref="xlink:type" fixed="title"/>
    <xs:attribute ref="xml:lang">
      <xs:annotation>
        <xs:documentation>
          xml:lang is not required, but provides much of the
          motivation for title elements in addition to attributes, and so
          is provided here for convenience.
        </xs:documentation>
      </xs:annotation>
    </xs:attribute>
  </xs:complexType>

  <xs:element name="resource" type="xlink:resourceType" abstract="true"/>

  <xs:complexType mixed="true" name="resourceType">
    <xs:sequence>
      <xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
    </xs:sequence>
    <xs:attribute ref="xlink:type" fixed="resource"/>
    <xs:attribute ref="xlink:role"/>
    <xs:attribute ref="xlink:title"/>
    <xs:attribute ref="xlink:label"/>
  </xs:complexType>

  <xs:element name="locator" type="xlink:locatorType" abstract="true"/>

  <xs:complexType name="locatorType">
    <xs:sequence>
      <xs:element ref="xlink:title" minOccurs="0" maxOccurs="unbounded"/>
    </xs:sequence>
    <xs:attribute ref="xlink:type" fixed="locator"/>
    <xs:attribute ref="xlink:href" use="required"/>
    <xs:attribute ref="xlink:role"/>
    <xs:attribute ref="xlink:title"/>
    <xs:attribute ref="xlink:label">
      <xs:annotation>
        <xs:documentation>
          label is not required, but locators have no particular
          XLink function if they are not labeled.
        </xs:documentation>
      </xs:annotation>
    </xs:attribute>
  </xs:complexType>

  <xs:element name="arc" type="xlink:arcType" abstract="true"/>

  <xs:complexType name="arcType">
    <xs:sequence>
      <xs:element ref="xlink:title" minOccurs="0" maxOccurs="unbounded"/>
    </xs:sequence>
    <xs:attribute ref="xlink:type" fixed="arc"/>
    <xs:attribute ref="xlink:arcrole"/>
    <xs:attribute ref="xlink:title"/>
    <xs:attribute ref="xlink:show"/>
    <xs:attribute ref="xlink:actuate"/>
    <xs:attribute ref="xlink:from"/>
    <xs:attribute ref="xlink:to">
      <xs:annotation>
        <xs:documentation>
          from and to have default behavior when values are missing
        </xs:documentation>
      </xs:annotation>
    </xs:attribute>
  </xs:complexType>

</xs:schema>