Example: Link redirection

A company wants to use a common DITA topic for information about recycling: recycling.dita. However, the topic contains a cross-reference to a topic that needs to be unique for each product line; each such topic contains product-specific URLs.

1. The editing team creates a recycling.dita topic that includes a cross-reference to the product-specific topic. The cross reference is implemented using a key reference:

   <xref keyref="product-recycling-info" href="generic-recycling-info.dita"/>

   The value of the @href attribute provides a fallback in the event that a product team forgets to include a key definition for "product-recycling-info".

2. Each product documentation group creates a unique key definition for "product-recycling-info". Each group authors the key definition in a DITA map, for example:

   <map>
     <!-- ... -->
     <keydef keys="product-recycling-info" href="acme-server-recycling.dita"/>
     <!-- ... -->
   </map>

   Each team can use the recycling.dita topic, and the cross reference in the topic resolves differently for each team.

3. A year later, there is an acquisition. The newly-acquired team wants to reuse Acme's common material, but it needs to direct its users to an external Web site that lists the URLs, rather than a topic in the product documentation. Their key definition looks like the following:

   <topicref  keys="product-recycling-info" 
                     href="http://acme.example.com/server/recycling" 
                     scope="external" format="html"/>
    

   When newly-acquired team uses the recycling.dita topic, it resolves to the external Web site; however for all other teams, the cross reference in the topic continues to resolves to their product-specific topic.

4. A new product team is formed, and the team forgets to include a key definition for "product-recycling-info" in one of their root maps. Because the cross reference in the recycling.dita topic contains a value for the @href attribute, the link falls back to generic-recycling-info.dita, thus avoiding a broken cross reference in the output.