Subsetting and customizing DITA (1250 words)

Subsetting versus specialization

To help clarify the difference in meaning between subsetting and specialization, consider an example that relates to the use of the 26 characters of the traditional English alphabet; that is, the letters A through Z. Generally, the idea of subsetting is similar to that of removing letters of the alphabet.

Therefore, subsetting, in the context of this document, means to remove or reorganize elements, attributes and attribute values to customize the way that options are presented, while ensuring all the DITA specifications are followed. Specialization is the general process by which additional elements are added to the DITA specification to allow for custom development of new information types.

Why subset and modify DITA

There are numerous reasons to consider customizing the DITA specification either through subsetting or through specialization. The three main reasons to subset include changing default tags, modifying the order or elements and adjusting the frequency of element use.

Default tag set

The default tags in the DITA specification include close to 200 elements. In many cases, tags provide features that are not required in your documentation or provide undesired redundancy. Many tags can be removed from the architecture and still leave all the structure authors need. This can be done without specialization.

Default element order

The order of elements in the DITA specification is incredibly flexible. This means that elements can be inserted in a variety of ways. The result is documents that allow writers the freedom to write. However, that freedom may result in writers skipping some elements or inserting others in an order that doesn’t adhere to your style guide. Modifications to the default element order allow restrictions to the organization of information. If this still adheres to the principles of the DITA specification your content remains compliant and your authors have a guided workflow.

Default element frequency

Many of the elements in the DITA specification allow child elements to appear with no restrictions. This means that, basically, authors can insert a wide variety of elements as often as desired. Ironically, this may result in undesired content, such as a step made up of a cmd, followed by an unlimited number of info child elements.

Sample subsetting of a DITA element

As a practical example of subsetting within the DITA specification, consider the step element. This element has numerous default child elements with few limitations placed upon them. By defining a subset of the step element we allow authors to create content while ensuring specific guidelines are followed. This ensures clear content is created within the DITA specification. All output is also fully compliant with the DITA specification. We therefore enforce a custom style of writing while following the DITA specification.

Default rule of step

Before we modify any elements, let’s begin by reviewing the default rules that the DITA specification enforces when working with the element step. The step element specifies: cmd then (info or substeps or tutorialinfo or stepxmp or choicetable or choices) (0 or more) then (stepresult) (optional).

The step contains numerous elements; some of which repeat and appear in an order that may not be repeated the next time the element step is used. By developing a custom rule additional restrictions can be enforced for consistency within your organization.

Custom rule for step

An example of a custom definition of step is seen below:

cmd, (info, choices?)?

The step contains a required cmd element. After the cmd there is a single info and a choices element. Nothing beyond this limited subset is allowed. Authors can not insert examples, multiple strings for info, numerous choices and more. The restriction helps to ensure consistency and provides more detailed guidance for each of the authors when working with a step.

Result of subsetting step

The result of the customization is a document set that is more professional, consistent and easier to manage. Editing and translation are simplified as there are fewer decisions that need to be made based on writing style.

Subsetting tags

There are close to 200 tags in the DITA specification. One of the easiest things you can do to make a DITA implementation simpler is to reduce the number of tags.

High level DITA elements

Numerous high level elements exist in the DITA specification and several can be safely removed when subsetting. It is important to first plan your document set and then begin to subset as the removal of high level elements and all associated child element is difficult to undo later. Also ensure that any element that is removed is not required elsewhere in the DITA specification. If it is, ensure you make appropriate modifications in all locations.

Common attributes

There are also several attributes that are commonly used throughout the DITA specification that may not be required. As with elements, it is important to plan your document set and then begin to subset. Remember that many of the attributes are reused throughout the DITA specification and it may be better to remove them on an element by element basis rather than removing them from the DITA specification completely.

Subsetting occurrence indicators and order

The frequency of elements in the DITA specification can be subset. Since the majority of elements are optional, removing them poses no significant impact in the compliance of your content with the DITA specification.

Drawbacks to subsetting

There are two key drawbacks to consider before subsetting: tab limitation and stricter rule requirements. If a DITA implementation is well planned neither should be a major problem in managing the way DITA is used.

Tag limitation

While subsetting helps to implement a stricter implementation of the DITA standard, it also deviates from it. By only supporting a key set of tags you restrict the ability to import other content that complies with the DITA specification.

Stricter rule requirements

By redefining the order of elements and their frequency, you effectively rule out some combinations of elements that others may use. In doing so, you may be limiting the usefulness of content that others provide that match the DITA specification.

Conclusion

Subsetting the DITA specification and modifying the default rules can provide many benefits to an organization. A restricted set of elements reduces the need to develop formatting and transformation rules for all possible combinations of elements. It also allows organizations to further control the types of content used and the way that they are used. This results in far more consistent documentation.

Tools used to develop this article

As the saying goes “we eat our own dog food”. In an effort to prove that DITA can be used to author content, and to deliver it in numerous formats, we created this entire article using readily available tools. Content was converted as required via numerous transforms provided with the DITA toolkit.