Subject scheme maps can define controlled values for DITA attributes without having to define specializations or constraints. The list of available values can be modified quickly to adapt to new situations.
Each controlled value is defined using a <subjectdef>
element,
which is a specialization of the <topicref>
element. The
<subjectdef>
element is used to define both a subject category and a list of controlled values. The
parent <subjectdef>
element defines the category, and the
children <subjectdef>
elements define the controlled values.
<topicmeta>
element to clarify the meaning of a value:<navtitle>
element can provide a more readable value
name.<shortdesc>
element can provide a definition.In addition, the <subjectdef>
element can reference a more
detailed definition of the subject, for example, another DITA topic or an external
resource..
The following behavior is expected of processors:
The following code fragment illustrates how a subject definition can provide a richer level of information about a controlled value:
<subjectdef keys="terminology" href="https://www.oasis-open.org/policies-guidelines/keyword-guidelines">
<subjectdef keys="rfc2119" href="rfc-2119.dita">
<topicmeta>
<navtitle>RFC-2119 terminology</navtitle>
<shortdesc>The normative terminology that the DITA TC uses for the DITA specification</shortdesc>
</topicmeta>
</subjectdef>
<subjectdef keys="iso" href="iso-terminology.dita">
<topicmeta>
<navtitle>ISO keywords</navtitle>
<shortdesc>The normative terminology used by some other OASIS technical committees</shortdesc>
</topicmeta>
</subjectdef>
</subjectdef>
The content of the <navtitle>
and
<shortdesc>
elements provide additional information that
a processor might display to users as they select attribute values or classify
content. The resources referenced by the @href
attributes provide
even more detailed information; a processor might render clickable links as part of
a user interface that implements a progressive disclosure strategy