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.