Online. XML

Published on Tuesday, June 3, 1997 by Gideon Ariel

Extensible Markup Language

APAS/Wizard makes use of XML to describe its protocol and report templates. XML is the Extensible Markup Language. It is designed to improve the functionality of the Web by providing more flexible and adaptable information identification.

It is called extensible because it is not a fixed format like HTML (a single, predefined markup language). Instead, XML is actually a ‘metalanguage’ �a language for describing other languages�which lets you design your own customized markup languages for limitless different types of documents. XML can do this because it’s written in SGML, the international standard metalanguage for text markup systems (ISO 8879).

What is XML?

  • XML stands for EXtensible Markup Language
  • XML is a markup language much like HTML
  • XML was designed to describe data
  • XML tags are not predefined. You must define your own tags
  • XML uses a Document Type Definition (DTD) or an XML Schema to describe the data
  • XML with a DTD or XML Schema is designed to be self-descriptive

The main difference between XML and HTML

XML was designed to carry data.

XML is not a replacement for HTML.
XML and HTML were designed with different goals:

XML was designed to describe data and to focus on what data is.
HTML was designed to display data and to focus on how data looks.

HTML is about displaying information, while XML is about describing information.

XML does not DO anything

XML was not designed to DO anything.

XML was not designed to DO anything.

Maybe it is a little hard to understand, but XML does not DO anything. XML was created to structure, store and to send information.

Check out the following protocol definition stored as XML:

<protocol id="demo" name="APAS/Wizard Demo Protocol">
  <apas3d id="file1" name="Discus Thrower" />

This XML document does not DO anything. It is just pure information wrapped in XML tags. APAS/Wizard will use this in determining which questions to ask, or how to generate a report.

XML is free and extensible

XML tags are not predefined. You must “invent” your own tags.

XML tags are not predefined. You must “invent” your own tags.

The tags used to mark up HTML documents and the structure of HTML documents are predefined. The author of HTML documents can only use tags that are defined in the HTML standard (like <p>, <h1>, etc.).

XML allows the author to define his own tags and his own document structure.

The tags in the example above (like <to> and <from>) are not defined in any XML standard. These tags are “invented” by the author of the XML document.

XML is a complement to HTML

XML is not a replacement for HTML.

It is important to understand that XML is not a replacement for HTML. In future Web development it is most likely that XML will be used to describe the data, while HTML will be used to format and display the same data.

My best description of XML is this: XML is a cross-platform, software and hardware independent tool for transmitting information.

XML in future Web development

XML is going to be everywhere.

We have been participating in XML development since its creation. It has been amazing to see how quickly the XML standard has been developed and how quickly a large number of software vendors have adopted the standard.

We strongly believe that XML will be as important to the future of the Web as HTML has been to the foundation of the Web and that XML will be the most common tool for all data manipulation and data transmission.