XML Basics

The loftier the building, the deeper must the foundation
be laid. - Thomas Kempis.

What is XML? The typical definition of eXtensible Markup Language (XML):

XML is a new World Wide Web Consortium (W3C⁴) specification. XML is a pared-down version of SGML, designed especially for Web documents. It enables developers to create their own customized tags to provide functionality not available through HTML.[5]

This definition provides a lot of information about XML, but it obviously was written by someone who lacks an understanding of XML and its capabilities. XML was designed as a database metalanguage[4]. It was designed as a means to structure content so it could be put into and be retrieved from a database in a form that was useful for content reuse. Information content can be text, graphics, audio, video, or complex constructs of all these learning components.

The principal difference between XML and HTML is that the former uses "smart tags." Smart tags convey information about the content they contain. Because of this, you can use the structure you create to put your content into an easily retrievable form. One exciting aspect of XML is the ability to define your content your way, creating custom tags for different kinds of instructional objects such as objectives, test questions, feedback and other common components of the training content[3].

Your content management system reads the smart tags and parses your content into useful chunks that you can assemble into subsequent documents. When you need the same (or similar) content, you construct a query of your content database. You then review the resulting content and if it matches your current use, you use it. If you find nothing useful, you add new content for your current document - and future use.

By using smart tags, it is also possible to define very specific criteria for making recursive changes. A branding change, which might take weeks to implement across an entire curriculum can be implemented in minutes. Editorial and style changes can be very exactly implemented in the precise circumstances defined by the editors. Legal reviews can be conducted on exemplar text, which is then recursively edited throughout the content library.

Each of the content elements is consistently tagged so that it fits together with other elements to form consistent document instances. In other words, each content object contains an introduction, main matter, illustrations (if any), conclusion and transitions. Several content objects are aggregated to form a document instance. Given a different use, it may be necessary to slightly modify some of the introductory or transitional materials. You also can structure your learning objects so that they can be specifically relevant to different user groups or to audiences of different aptitudes. The next document instance you require may contain the same content objects, which have been modified, just a little here and there, to meet the requirements of the different audience.

The process of defining these structural components is analogous to creation of animation cells from layers. Each layer contains a different quality of information pertaining to the same object. These objects are then added together to produce an instance of learning delivery.

There are three main components of XML objects with which instructional designers need to be concerned: XML, DTD and XSLT. The XML file contains the content, just the content and only the content. The Document Type Definition (DTD) specifies how the XML is structured. The XML Style sheet (XSLT) contains all the formatting information for the output document instance.