Subject Scheme

The Subject Scheme Map is a specialized DITA Map that defines allowed attribute values.

map.ditamap

The map.ditamap references the Subject Scheme Map subjectScheme.ditamap. The attributes values are mapped with keys and are therefore available in all topics of the map.ditamap.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE map PUBLIC "-//OASIS//DTD DITA Map//EN" "map.dtd">
<map>
  <title>Subject Scheme Map Example</title>
  <topicref href="topic.dita"/>
  <mapref href="subjectScheme.ditamap"/>
</map>

subjectScheme.ditamap

The subjectScheme.ditamap defines the attribute values. An attribute value is specified using the @keys attribute of a <subjectdef> element. The key is then used to pull and map its children to an attribute. In this case, in the <enumerationdef> element, the attribute values of the os key are binded to the attribute @platform

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE subjectScheme PUBLIC "-//OASIS//DTD DITA Subject Scheme Map//EN" "subjectScheme.dtd"> 
<subjectScheme>
  <!-- The key "os" is the top level attribute value -->
  <subjectdef keys="os" navtitle="Operating system">
    <subjectdef keys="android" navtitle="Android">
      <subjectdef keys="android5" navtitle="Android 5 Lollipop"/>
      <subjectdef keys="android6" navtitle="Android 6 Marshmallow"/>
      <subjectdef keys="android7" navtitle="Android 7 Nougat"/>
    </subjectdef>
    <subjectdef keys="ios" navtitle="iOS">
      <subjectdef keys="ios8" navtitle="iOS 8 Donner"/>
      <subjectdef keys="ios9" navtitle="iOS 9 Eagle"/>
      <subjectdef keys="ios10" navtitle="iOS 10 Whitetail"/>
    </subjectdef>
    <subjectdef keys="windows" navtitle="Windows">
      <subjectdef keys="windows7" navtitle="Windows 7"/>
      <subjectdef keys="windows8" navtitle="Windows 8"/>
      <subjectdef keys="windows10" navtitle="Windows 10"/>
    </subjectdef>  
  </subjectdef>
  <!-- The <enumerationdef> element binds the values of the "os" key to the attribute "platform" -->
  <enumerationdef>
    <attributedef name="platform"/>
    <subjectdef keyref="os"/>
  </enumerationdef>
</subjectScheme>

topic.dita

If the topic.dita is opened in the scope of the map.ditamap map, the values for the @platform attribute are pulled from the Subject Scheme Map.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
<topic id="topic">
    <title>topic</title>
    <body>
        <p platform="android7"/>
    </body>
</topic>