XML Overview

April 30, 1997

XML stands for eXtensible Markup Language. It is a simplified subset of SGML (Standard Generalized Markup Language, ISO 8879), specifically designed for Web applications. XML provides three key advantages over HTML:

• Extensibility: Information providers can define new tags and attribute names specific to their applications.
• Structure: Document structures can be nested to any level of complexity.
• Validation: Applications can quickly check XML documents for structural validity without referring to an external definition of terms.

Here's an example of how XML might be used: A medical application includes a patient medical history document type, which includes a <medical description> structure, an <allergy> structure within the medical description, and <allergen> tags within the allergy structure. The medical application validates the data to make sure that the <allergen> tags, if present, are in the <allergy> and <medical description> structures, and not in the <patient address> structure.

Will XML work?

Yes. XML is based on proven SGML technology, which is already in use at places such as the Library of Congress.

Is XML based on standards?

Yes. There's an XML working group at the World Wide Web Consortium (W3C). They published their latest working draft in March 1997. It's available on http://www.w3.org/pub/WWW/TR/WD-xml.html .

Does XML have broad industry support?

Yes. Led by Microsoft, XML is supported by Sun, SoftQuad, NCSA, Hewlett-Packard, and now Netscape (as of April 1997), among other companies.

Will Microsoft support XML in Internet Explorer?

Internet Explorer version 4.0 will support a few XML applications (such as CDF). Microsoft will be supporting XML in future versions of Internet Explorer.