Friday, April 25, 2008

Context-driven Transclusion

I recently had to implement a really interesting set of functionality for a client where the core content could include supplementary content that was edited and maintained separately. Since supplemental content could change on a regular basis, we wanted to ensure that the supplemental content was always up to date within the core content. The core DITA topic templates could be reused in different map templates that formed the basis of a final form publication, and the client wanted slightly different supplement content to be displayed based on which map template it was contained in.

Conref wouldn't work since we couldn't point to a static resource. Applying a profile also wouldn't since the inclusion wasn't based on a static profile type and also had another negative side effect: by assign the value with a topic, the context of any dynamic transclusion is limited by the current known universe of map templates. Since this client would continue to add/remove/change the map templates, the underlying topic template would have to be touched each time a map template was changed.

The approach I devised was to assign each supplement block with one required and one optional attribute:
  • name: This would identify the supplement with an identifier that could be referenced within the topic
  • map-type: This is a "conditional" attribute that identifies that type of map this particular supplement will appear in. If the supplement didn't include this attribute, it would be considered "global" and would appear in all map types.

The supplement itself was a domain specialization that allowed me to create a specialized topic that contained nothing but supplements, and to embed the domain into my main content topic specialization. Here's a quick sample of the supplement content:

<!-- global supplement: appears in all map types -->
<supplement name="introduction">

<!-- conditional supplement: appears in specified map types -->
<supplement name="getting-started" map-type="type1">
Do steps 1, 2, 3 and 4
<supplement name="getting-started" map-type="type2">
Do steps 1, 3, 5 and 7

So in each of my content topics, I created an anchor using the same element name, but this time I use a third attribute I created on the supplement called sup-ref. The sup-ref attribute acted like an IDREF by referencing a supplement element with the same name. Let's assume I have a topic with a file name of "topic1.dita":

<mytopic id="topic1">
<supplement sup-ref="introduction"/>
<supplement sup-ref="getting-started"/>
So in this case, I have supplements that the reference content for introduction which is a global (unconditional) supplement, and a second supplement, getting-started, that is conditional and will only be included into my content topic if the topic is referenced in the context of a map-type with a value that matches.

Now let's assume that I have two different map types that are defined by an attribute called map-type (I could have also created two separate map specializations with different names depending on what you need, your mileage may vary). This attribute stores a defined map's type name.

<mymap map-type="type1">
<topicref href="topic1.dita"/>

This attribute is primarily used as metadata for identifying and organizing maps within a content store (CMS, XML Database, etc.), but we can also use it for driving our transclusion.

In our XSLT, we simply create a variable that stores the map's map-type value:

<xsl:variable name="map.type" select="@map-type">
When we process our content topic and encounter our supplement reference, we perform a two-stage selection that
  • collects all supplements with a name attribute that matches the current sup-ref attribute - we do this because we don't know yet if the supplement source is global or context-specific.
  • With this collection, we refine our search by testing if there are more than one supplement elements, if so, we filter the search by obtaining the supplement that has a map-type attribute that matches our map.type variable. Otherwise, we run a simple test to see if our single supplement is intended for a specific map context or not. If not, include the supplement. If there is a map context, we can emit an error indicating that there isn't a matching supplement.
If we have a match, we replace the anchor supplement element in our content topic, with the supplement element in our external source.

The cool part of all of this is that I can keep the supplemental material separate so that it can be edited and updated when it needs and I can supply different supplemental content to the content topic based on its context as a member of a map and the map's type.

While this is a specific scenario in DITA (the names and functions of the elements have been changed for client confidentiality), the same approach can also be applied to other scenarios that require similar functionality for virtually any XML grammar!

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