compromise xlink schema (loc + w3c)

xlink.xsd

<?xml version="1.0" encoding="UTF-8"?>
<!-- METS XLink Schema, v. 2, Nov. 15, 2004 -->
<schema targetNamespace="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2001/XMLSchema" xmlns:xlink="http://www.w3.org/1999/xlink" elementFormDefault="qualified">

<!-- import from w3c xlink schema has to go first -->
 <import namespace="http://www.w3.org/XML/1998/namespace" schemaLocation="http://www.w3.org/2001/xml.xsd"/>
 
 <!-- attribute definitions from loc xlink schema superceded by ones from w3c schema -->
 
 <!-- attribute groups from LOC xlink schema https://www.loc.gov/standards/xlink/xlink.xsd -->
 
  <!--  global attributes  --> 
  <attributeGroup name="simpleLink">
    <attribute name="type" type="string" fixed="simple" form="qualified" /> 
    <attribute ref="xlink:href" use="optional" /> 
    <attribute ref="xlink:role" use="optional" /> 
    <attribute ref="xlink:arcrole" use="optional" /> 
    <attribute ref="xlink:title" use="optional" /> 
    <attribute ref="xlink:show" use="optional" /> 
    <attribute ref="xlink:actuate" use="optional" /> 
  </attributeGroup>
  <attributeGroup name="extendedLink">
    <attribute name="type" type="string" fixed="extended" form="qualified" /> 
    <attribute ref="xlink:role" use="optional" /> 
    <attribute ref="xlink:title" use="optional" /> 
  </attributeGroup>
  <attributeGroup name="locatorLink">
    <attribute name="type" type="string" fixed="locator" form="qualified" /> 
    <attribute ref="xlink:href" use="required" /> 
    <attribute ref="xlink:role" use="optional" /> 
    <attribute ref="xlink:title" use="optional" /> 
    <attribute ref="xlink:label" use="optional" /> 
  </attributeGroup>
  <attributeGroup name="arcLink">
    <attribute name="type" type="string" fixed="arc" form="qualified" /> 
    <attribute ref="xlink:arcrole" use="optional" /> 
    <attribute ref="xlink:title" use="optional" /> 
    <attribute ref="xlink:show" use="optional" /> 
    <attribute ref="xlink:actuate" use="optional" /> 
    <attribute ref="xlink:from" use="optional" /> 
    <attribute ref="xlink:to" use="optional" /> 
  </attributeGroup>
  <attributeGroup name="resourceLink">
    <attribute name="type" type="string" fixed="resource" form="qualified" /> 
    <attribute ref="xlink:role" use="optional" /> 
    <attribute ref="xlink:title" use="optional" /> 
    <attribute ref="xlink:label" use="optional" /> 
  </attributeGroup>
  <attributeGroup name="titleLink">
    <attribute name="type" type="string" fixed="title" form="qualified" /> 
  </attributeGroup>
  <attributeGroup name="emptyLink">
    <attribute name="type" type="string" fixed="none" form="qualified" /> 
  </attributeGroup>

<!-- start of stuff copied from w3c xlink schema http://www.w3.org/1999/xlink.xsd -->

 <annotation>
  <documentation>This schema document provides attribute declarations and
attribute group, complex type and simple type definitions which can be used in
the construction of user schemas to define the structure of particular linking
constructs, e.g.
<![CDATA[
<schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:xl="http://www.w3.org/1999/xlink">

 <import namespace="http://www.w3.org/1999/xlink"
            location="http://www.w3.org/1999/xlink.xsd">

 <element name="mySimple">
  <complexType>
   ...
   <attributeGroup ref="xl:simpleAttrs"/>
   ...
  </complexType>
 </element>
 ...
</schema>]]></documentation>
 </annotation>

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 <simpleType name="labelType">
  <restriction base="NCName"/>
 </simpleType>

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

 <simpleType name="fromType">
  <restriction base="NCName"/>
 </simpleType>

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

 <simpleType name="toType">
  <restriction base="NCName"/>
 </simpleType>

 <attributeGroup name="simpleAttrs">
  <attribute ref="xlink:type" fixed="simple"/>
  <attribute ref="xlink:href"/>
  <attribute ref="xlink:role"/>
  <attribute ref="xlink:arcrole"/>
  <attribute ref="xlink:title"/>
  <attribute ref="xlink:show"/>
  <attribute ref="xlink:actuate"/>
 </attributeGroup>

 <group name="simpleModel">
  <sequence>
   <any processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
  </sequence>
 </group>

 <complexType mixed="true" name="simple">
  <annotation>
   <documentation>
    Intended for use as the type of user-declared elements to make them
    simple links.
   </documentation>
  </annotation>
  <group ref="xlink:simpleModel"/>
  <attributeGroup ref="xlink:simpleAttrs"/>
 </complexType>

 <attributeGroup name="extendedAttrs">
  <attribute ref="xlink:type" fixed="extended" use="required"/>
  <attribute ref="xlink:role"/>
  <attribute ref="xlink:title"/>
 </attributeGroup>

 <group name="extendedModel">
   <choice>
    <element ref="xlink:title"/>
    <element ref="xlink:resource"/>
    <element ref="xlink:locator"/>
    <element ref="xlink:arc"/>
  </choice>
 </group>

 <complexType name="extended">
  <annotation>
   <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.
   </documentation>
  </annotation>
  <group ref="xlink:extendedModel" minOccurs="0" maxOccurs="unbounded"/>
  <attributeGroup ref="xlink:extendedAttrs"/>
 </complexType>

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

 <attributeGroup name="titleAttrs">
  <attribute ref="xlink:type" fixed="title" use="required"/>
  <attribute ref="xml:lang">
   <annotation>
    <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.
    </documentation>
   </annotation>
  </attribute>
 </attributeGroup>

 <group name="titleModel">
  <sequence>
   <any processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
  </sequence>
 </group>

 <complexType mixed="true" name="titleEltType">
  <group ref="xlink:titleModel"/>
  <attributeGroup ref="xlink:titleAttrs"/>
 </complexType>

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

 <attributeGroup name="resourceAttrs">
  <attribute ref="xlink:type" fixed="resource" use="required"/>
  <attribute ref="xlink:role"/>
  <attribute ref="xlink:title"/>
  <attribute ref="xlink:label"/>
 </attributeGroup>

 <group name="resourceModel">
  <sequence>
   <any processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
  </sequence>
 </group>

 <complexType mixed="true" name="resourceType">
  <group ref="xlink:resourceModel"/>
  <attributeGroup ref="xlink:resourceAttrs"/>
 </complexType>

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

 <attributeGroup name="locatorAttrs">
  <attribute ref="xlink:type" fixed="locator" use="required"/>
  <attribute ref="xlink:href" use="required"/>
  <attribute ref="xlink:role"/>
  <attribute ref="xlink:title"/>
  <attribute ref="xlink:label">
   <annotation>
    <documentation>
     label is not required, but locators have no particular
     XLink function if they are not labeled.
    </documentation>
   </annotation>
  </attribute>
 </attributeGroup>

 <group name="locatorModel">
  <sequence>
   <element ref="xlink:title" minOccurs="0" maxOccurs="unbounded"/>
  </sequence>
 </group>

 <complexType name="locatorType">
  <group ref="xlink:locatorModel"/>
  <attributeGroup ref="xlink:locatorAttrs"/>
 </complexType>

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

 <attributeGroup name="arcAttrs">
  <attribute ref="xlink:type" fixed="arc" use="required"/>
  <attribute ref="xlink:arcrole"/>
  <attribute ref="xlink:title"/>
  <attribute ref="xlink:show"/>
  <attribute ref="xlink:actuate"/>
  <attribute ref="xlink:from"/>
  <attribute ref="xlink:to">
   <annotation>
    <documentation>
     from and to have default behavior when values are missing
    </documentation>
   </annotation>
  </attribute>
 </attributeGroup>

 <group name="arcModel">
  <sequence>
   <element ref="xlink:title" minOccurs="0" maxOccurs="unbounded"/>
  </sequence>
 </group>

 <complexType name="arcType">
  <group ref="xlink:arcModel"/>
  <attributeGroup ref="xlink:arcAttrs"/>
 </complexType>

</schema>