Variables using conref and filtering

Single-source publishing relies heavily on the concept of variables. While DITA does not have a specifically named variables feature, it does readily support variables functionality.

In the context of single-source publishing, a variable is an element that is used throughout the content of a publication in place of a normal fixed unit of text. When the document is published, the variable element is replaced with a nominated phrase or block of text. Variables allow numerous text changes to be made with very little effort.

For example, documentation might be required for a product sold under two brand names, Legend and Liberty. Instead of hard-coding the product name, a variable of brand_name might be used whenever the product is mentioned in the text. During the publishing of the documentation for the Liberty brand, the brand_name variable is replaced with the word "Liberty."

In DITA, variables are implemented through the conref and ditaval filtering features. The variable is coded as conreffed element, such as <ph conref="abc.dita#product" />. The conref source is coded using metadata attributes that can be used for filtering, such as:

<ph id="product>
  <ph product="Liberty">Liberty</ph>
  <ph product="Legend">Legend</ph>
</ph>

When the content is published, the conditional filtering in the ditaval can be set so that only the applicable product name element is included in the output.