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XML Basics

What is XML? The typical definition of XML:

.75in .5in XML is a World Wide Web Consortium (W3C1) standard for Internet markup languages. XML is called 'extensible' because it is not a fixed format like Hypertext Markup Language (HTML). It is designed to enable the use of Standard Generalized Markup Language (SGML) on the World Wide Web. It is an abbreviated version of SGML, making it easier to define document types, and to make it easier for programmers to write programs to handle them. It omits the more complex and less-used parts of SGML in return for the benefits of being easier to write applications for, easier to understand, and more suited to delivery and interoperability over the Web.

This definition provides a lot of information about XML, but it was obviously written by someone who lacks an understanding of what XML is and what it is for. XML was designed as a database metalanguage[7]. It was designed as a means to structure information content so that 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 of 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 all the other common components of training content[5].

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 next time.

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

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 strung together to produce an instance of learning delivery.

\includegraphics[width=5in]{Images/outline.eps}

There are three main components of XML objects that instructional designers need to be concerned with: 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 instance document.



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next up previous index
Next: Document Type Definitions (DTD) Up: XML and Code Reuse Previous: Terminology   Index
root 2003-07-21