What is XML?

by **Adminkunlex** Sun Jan 05, 2020 8:55 am

XML is a standard set of rules for writing documents
in a way that a computer can read them. It doesn't
say anything about what the documents mean, or
how they will be used.
Because tools to write and read XML exist in every
programming language, it has become a popular way
to transmit data between computer programs,
especially across networks.
A programmer or information worker can create an
"XML language" that describes any kind of data that
they need; for example, a word processing document
(e.g. Microsoft Office OpenXML), a web page (XHTML),
or a series of updates to a website (RSS, or Atom).
While these documents share a basic set of encoding
rules, their content can be completely unrelated and
programs designed to read them are unlikely to be
able to work together without additional work.
XML documents are Unicode text, meaning that they
can represent any human language in a standard
way. XML documents are hierarchical, meaning that
they organize data into a series of items and sub-
items.
Derivative Languages and Tools
Because XML is such a general-purpose set of rules, it
has been the basis of a number of derivative
languages and tools. These languages act on, or
describe, XML documents in a general way. A very
incomplete list of prominent examples include:
XSL, the Extensible Stylesheet Language, which is a
general-purpose transformation language. An XSL
document describes how to process the data in an
XML document in order to produce some output -
another XML document, a text document, a table of
data, or even an image.
DTD, XML Schema, Relax NG, Schematron, and other
schema languages. These languages describe the
structure and content of an XML document in a
way that allows a computer to determine whether
the document is "valid", meaning that it satisfies
the constraints of the schema.
XPath is a programming syntax that allows the
description of an exact subset of the data in an XML
document. It is widely used in other XML-related
tools, including XSL and XML Schema.
Additional Reading
The Wikipedia has an excellent and wide-ranging
article on the topic at
http://en.wikipedia.org/wiki/XML
The Internet Engineering Task Force has a set of
recommendations on the use of XML within internet protocols:
http://www.ietf.org/rfc/rfc3470.txt

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