XML (eXtensible Markup Language): An Overview

As web developers know all too well, basic HTML (HyperText Markup Language) doesn't provide any structure to Web pages, and the formatting is mixed with the content. To allow Web pages to be structured for automated processing (e.g. electronic commerce), the World Wide Web Consortium (W3C) developed an enhancement to HTML. The result were two new languages; one was XSL (eXtensible Style Language), and the other was XML (eXtensible Markup Language), a system for defining, validating, and sharing document formats on the Web.

XML is best known to many bloggers and Netizens as RSS (Rich Site Summary/Really Simple Syndication), which is actually a lightweight XML format used to share headlines and blog feeds.

History

The W3C, an organization devoted to developing the Web and standardizing protocols, formed an XML Working Group chaired by Jon Bosak of Sun Microsystems in 1996. Several key industry players who were also included in the working group were Adobe, Hewlett-Packard, Microsoft, Netscape, and Fuji Xerox.

The group published a working draft for XML in November of the same year. Two years later, the W3C announced the release of the XML 1.0 specification.

The year 1999 found the release of two W3C Recommendations on XML. The first was entitled Namespaces on XML, and the other was Associating Stylesheets with XML documents. In January of 2001, the Internet Engineering Task Force (IETF) released a Proposed Standard on XML Media Types.

Profile

XML is an open, human-readable text format derived from the Standard Generalized Markup Language (SGML). Originally meant for large-scale electronic publishing, XML is now being used in the exchange of various types of data on the Web and elsewhere. It is also becoming a language of choice for communication between application programs.

The XML Working Group's design goals (taken from the W3C website) for XML were:

XML shall be straightforwardly usable over the Internet.

XML shall support a wide variety of applications.

XML shall be compatible with SGML.

It shall be easy to write programs that process XML documents.

The number of optional features in XML is to be kept to the absolute minimum, ideally zero.

XML documents should be human-legible and reasonably clear.

The XML design should be prepared quickly.

The design of XML shall be formal and concise.

XML documents shall be easy to create.

Terseness in XML markup is of minimal importance.

The markup language describes XML documents, which are a class of data objects. Moreover, XML also describes the behavior of software modules called XML processors. These are used to read XML documents and provide access to their content and structure.

Syntax

Those familiar enough with HTML will find XML syntax a lot similar. However, don't assume that coding in XML is painlessly easy -- XML is stricter than HTML, and sloppy HTML coders will do well to remember that. Several reminders when coding in XML:

All elements must have a closing tag.

All elements must be properly nested.

All tags are case sensitive.

All attribute values must be enclosed in quotation marks.

A good hands-on tutorial on XML can be found at W3Schools.com.