XML for the absolute beginner

By Mark Johnson, ITworld.com |  Development



There's so much recent XML activity in the computer world that even an
article of this length can only skim the surface. Still, the whole
point of this article is to give you the context you need to use XML in
your Java program designs. This article also covers how XML operates
with existing Web technology, since many Java programmers work in such
an environment.


XML opens the Internet and Java programming to portable, nonbrowser
functionality. XML frees Internet content from the browser in much the
same way Java frees program behavior from the platform. XML makes
Internet content available to real applications.


Java is an excellent platform for using XML, and XML is an outstanding
data representation for Java applications. I'll point out some of
Java's strengths with XML as we go along.


Let's begin with a history lesson.


The origins of markup languages

The HTML we all know and love (well, that we know, anyway) was
originally designed by Tim Berners-Lee at CERN (le Conseil
Européen pour la Recherche Nucléaire,
or the
European Laboratory for Particle Physics) in Geneva to allow physics
nerds (and even non-nerds) to communicate with each other. HTML was
released in December 1990 within CERN, and became publicly available in
the summer of 1991 for the rest of us. CERN and Berners-Lee gave away
the specifications for HTML, HTTP, and URLs, in the fine old tradition
of Internet share-and-enjoy.


Berners-Lee defined HTML in SGML, the Standard Generalized Markup
Language. SGML, like XML, is a metalanguage -- a language used for
defining other languages. Each so-defined language is called an
application of SGML. HTML is an application of SGML.


SGML emerged from research done primarily at IBM on text document
representation in the late '60s. IBM created GML ("General Markup
Language"), a predecessor language to SGML, and in 1978 the
American National Standards Institute (ANSI) created its first version
of SGML. The first standard was released in 1983, with the draft
standard released in 1985, and the first standard was published in
1986. Interestingly enough, the first SGML standard was published
using an SGML system developed by Anders Berglund at CERN, the
organization that, as we have seen, gave us HTML and the Web.


SGML is widely used in large industries and governments such as in
large aerospace, automotive, and telecommunications companies. SGML is
used as a document standard at the United States Department of Defense
and the Internal Revenue Service. (For readers outside of the US, the
IRS are the tax guys.)


Albert Einstein said everything should be made as simple as possible,
and no simpler. The reason SGML isn't found in more places is that
it's extremely sophisticated and complex.

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