XML: An Introduction

 XML, An eXtensible markup Language -- is an exciting development in web technology. It is the youngest and most comprehensive of markup languages. (Markup refers to anything on a document that adds special meaning to a particular piece of text; for example, bold text is a form of markup).

 

XML got its name Extensible Markup Language from the characteristic that it is not restricted to a fixed set of tags, as is HTML (Hypertext Markup Language). An XML user creates his own tags according to need. A tag is a sequence of characters in a markup language used to provide information, such as formatting specifications, about a document.

 

Markup languages are roughly classified into three types:

* Stylistic - defines character presentation; for example bold, italics, underline, font etc.
* Structural – defines the structure of the document, such as heading and paragraphs.
* Semantic – informs us about the content of the data, like specifying a title.

 

Its History:
 

SGML (Standardized Generalized Markup Language) is the mother of all markup languages and has been in existence since the late 1960s. In 1986 it became an international standard for defining the markup languages. It was used to create other languages, including HTML, which is very popular for its use on the web. HTML was made by Tim Berners Lee in 1991. While on one hand SGML is very effective but complex, on the other, HTML is very easy, but limited to a fixed set of tags. This situation raised the need for a language that was as effective as SGML and at the same time as simple as HTML. This gap has now been filled by XML.

The development of XML started in 1996, when a team led by Jon Bosak of Sun Microsystems began work on a project for remolding and cutting the inessential parts of SGML. They took the best of SGML, guided by the experience with HTML, and produced something that was powerful, but much simpler to use. The World Wide Web Consortium also contributes to the creation and development of the standard for XML. The specifications for XML were laid down in just 26 pages, compared to the 500+ page specification that define SGML.

 

It's Usage
 

Although, XML looks like HTML, there is a world of a difference. While HTML specifies what each tag and attribute means and how the text defined by it will look in a browser, XML uses the tag only to delimit pieces of data, and leaves the interpretation of the data completely to the application that reads it.

 

For example, if we see “<b>” in an XML file, it may or may not mean bold (as in HTML) -- it may mean ’book’, ‘bank’ or anything else specified by the programmer. HTML is only a presentation technology -- it carries no description of the content held within its tags -- whereas in XML a programmer can describe the text in its own tag. Moreover we can specify the importance of a tag in XML so that a hierarchy of data can be represented, which is not possible in HTML.

Like HTML, both Netscape and Microsoft browsers support XML. As XML files are text files, it becomes easier for a programmer to debug applications.

 

But at the same time, being in a text format, XML files are always larger than comparable binary formats. XML is a family of technologies.

 

 XLINK is one of them, which describes a standard way to add hyperlinks to an XML file. XPOINTER and XFRAGMENTS are syntaxes for pointing to parts of an XML document. XSL is an advanced language for expressing style sheets. We can also use cascading style sheets (CCS) as we do in HTML. XML NAMSPACE is a specification that describes how to associate a URL with every single tag. XML SCHEMAS help to define the XML-based formats.


DOM is a standard set of functions called for manipulating XML files from a programming language. Math ML is a standard describing mathematics as a basis for machine communication. With adequate style-sheet support it would ultimately be possible for browsers to natively render mathematical expressions, which is not possible in HTML. XML encryption is a process name for encrypting and decrypting digital content. XML signatures provide integrity and message authentication for data of any type. These things are extensively used for providing security in applications.

XML protocol is used to develop technologies that allow two or more peers to communicate in a distributed environment, using XML as its encapsulation language. Nowadays we can find a number of quality sites made using XML. Use of XML can also be seen in B2B portals and it is also used in WAP development. WML (Wireless Markup Language) is derived from XML, which plays the primary role in the development of WAP applications.

The most novel feature of XML is that it is able to express complex data structures, and even distributed action, in terms of simple, punctuated streams of text. Any network component newer than the Abacus can send and receive XML; almost any processor has sufficient power to parse it. XML is license free, platform independent and well supported. Visual Studio .NET, Hailstorm, and the .NET platform, some of the latest products offered by Microsoft, are fully compatible with XML.

 

Many companies are using this language according to their needs. As this language can be used for various objectives, it can be seen on various platforms, in combination with different languages. XML is a key to the next-generation Internet, offering a way to unlock information so that it can be organised, programmed and edited – a way to distribute data in more useful ways to a variety of digital devices and allowing web sites to collaborate. Today XML is a young child developing various aspects of its personality; which of these would be the dominating trait to give it its final adult character could be anybody’s guess.