Beginning XML - Part 1 (An Introduction)

Coming straight to the point, XML stands for EXtensible Markup
Language. As the name suggests, it is a language that can be
molded according to the need of the hour. Personally, I don't
think calling it a language is justified, but I fanatically
follow the ordinance of the techie Gurus, and if they say it is a
language, then it is a language.

As is the case with the famous HTML, XML too is a markup
language, but its main power, unlike HTML, lies in the ability to
describe data without harassing the over-worked server. Since
most of the work is done on the client's machine (the person who
is running the browser), there is less strain on the server.

It uses DTDs (Document Type Definitions) to properly define and
organize data. But the presence of DTDs is not mandatory, and
their absence does not hinder the performance of the web page.

The most interesting thing I have found in XML is, the tags are
not pre-defined - you can create your own tags and use them as
and when required. XML specifies neither semantics nor a tag set.
In fact XML is really a meta-language for describing markup
languages. In other words, XML provides a facility to define tags
and the structural relationships between them. Since there's no
predefined tag set, there can't be any preconceived semantics.
All of the semantics of an XML document will either be defined by
the applications that process them or by style-sheets.

XML allows users to:

· bring multiple files together to form compound documents
· identify where illustrations are to be incorporated into text
files, and the format used to encode each illustration
· provide processing control information to supporting programs,
such as document validators and browsers
· add editorial comments to a file.

It is important to note, however, that XML is not:

· a predefined set of tags, of the type defined for HTML, that
can be used to markup documents
· a standardized template for producing particular types of
documents.

XML was not designed to be a standardized way of coding text: in
fact it is impossible to devise a single coding scheme that would
suit all languages and all applications. Instead XML is formal
language that can be used to pass information about the component
parts of a document to another computer system. XML is flexible
enough to be able to describe any logical text structure, whether
it be a form, memo, letter, report, book, encyclopedia,
dictionary or database.

The primary goal of XML is to enable SGML-coded data to be
served, received, and processed on the Web in the way that is as
easy as that currently made possible by use of the fixed SGML tag
set provided by HTML. Ok, SGML means Standard Generalized Markup
Language. SGML was designed in the 1980's as a tool to enable
technical documentation and other forms of publishable data to be
interchanged between authors, publishers and those responsible
for the production of printed copies of data sets. By providing a
formal definition of the component parts of a publishable
information set, SGML made it possible to verify the correct
transmission and receipt of interchanged data sets. It was soon
found that these techniques are applicable in areas other than
those directly related to publications. For example, SGML is
often used as a neutral data format when moving data between
databases as part of multinational projects.

XML has been designed for ease of implementation and for
interoperability with both SGML and HTML. Unlike early versions
of SGML and HTML, XML has been based from the very start on the
ISO 10646 Universal Multi-Octet Coded Character Set (UCS, which
includes the codes that make up the Unicode character set) so
that it can be used in all major trading nations.