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Metadata, conditional processing, and indexing
Indexing
DITA incorporates powerful features for indexing, including multi-level indexing, and see and see-also redirection. Index entries can be applied in the ditamap, in the topic prolog, and inline within the topic content.
Re-using index entries
You can create a special ditamap which has a sole purpose of being the container for common indexterm elements for re-use in the prolog section of topics (and the topicmeta section of ditamaps, if required) through the conref feature.

Introduction
Information types and topics
Topics are the building blocks of modular documents, and organising topics by semantic information types is one of the architectural features of DITA.
DITA map files
Syntax and mark-up
Language and punctuation
Graphics and figures
Cross-referencing
Cross-references are a means of binding individual topics into a coherent and navigable document.
Content re-use
Metadata, conditional processing, and indexing
- Conditional processing concepts
  When DITA content is processed to a reading format, rules to exclude or highlight some of the content can be defined in a ditaval file. This conditional processing requires metadata attributes to be set on DITA elements that may possibly be excluded or highlighted.
- Condition (or select) attributes
  The audience, platform, product, otherprops and rev attributes can be applied to most DITA elements. They are used for conditional processing, and are known as the condition (or select) attributes.
- Filtering and flagging
  Content marked with metadata attributes can be conditionally processed so that the content is filtered (excluded) or flagged (highlighted) in the published output.
- Other metadata
  In addition to the select attributes, DITA content includes many forms of metadata. These metadata elements and attributes are used to manage and organise topics, ditamaps and publications.
- Indexing
  DITA incorporates powerful features for indexing, including multi-level indexing, and see and see-also redirection. Index entries can be applied in the ditamap, in the topic prolog, and inline within the topic content.
  - Placement of indexterm elements
    The indexterm element is pure metadata, and does not display. You should place index entries in the prolog section of the topic, or in the topicmeta section of the topicref in the ditamap only if the term is specific to a particular publication.
  - Nesting index entries
    The technique of nesting indexterm elements can produce multi-level indexes in output documents.
  - Index see and see also
    Readers can be re-directed from a searched-for term to related terms in the index that provide further references. You can use the index-see and index-see-also indexing elements for this purpose.
  - Re-using index entries
    You can create a special ditamap which has a sole purpose of being the container for common indexterm elements for re-use in the prolog section of topics (and the topicmeta section of ditamaps, if required) through the conref feature.
The DITA documentation process
DITA authoring concepts
Moving from style-based authoring to a structured authoring methodology such as DITA requires a radically different approach to writing.

Re-using index entries

You can create a special ditamap which has a sole purpose of being the container for common indexterm elements for re-use in the prolog section of topics (and the topicmeta section of ditamaps, if required) through the conref feature.

Like most DITA elements, index elements can be re-used through the conref mechanism. There are good reasons why you might want to re-use index entries, including consistency of wording and punctuation, and reduced translation costs. (Even if used in more than one place, re-used index entries only have to be translated once in the conref source.)

You may find that you can better manage the re-use of index terms if they are stored in their own, standalone, ditamap. That index re-use ditamap will never be processed, and never embedded in another ditamap; it is only used for the purposes of re-use. Such a ditamap file should be named with a prefix of conref_source_. The ditamap could easily be used by many authors working in the same team.

The code for an index re-use ditamap would follow the pattern:

<map id="conref_index_reuse">
  <title>Index Term Re-use</title>
  <topicmeta>
    <keywords>
      <indexterm id="index_turbocharger">turbocharger</indexterm>
      <indexterm id="index_keypad_PIN">keypad
        <indexterm>PIN</indexterm>
      </indexterm>
      <indexterm id="index_immobiliser">immobiliser</indexterm>
      ...
    </keywords>
  </topicmeta>
</map>