Introduction to XML

The evolution of XML is due to the requirement for a platform independent tool for carrying information within and across the networks. XML’s temporal relationship to SGML (Standard Generalized Markup Language) and HTML (Hyper Text Markup Language) is depicted in the figure below.

XML was designed to transport and store data, with focus on what data is.

It removes two constraints which were holding back Web developments:

Ø  Dependence on a single, inflexible document type (HTML)

Ø  The complexity of SGML, whose syntax allows many powerful but hard-to-program options.

Introduction on XML:

·         XML stands for eXtensible Markup Language

·         XML is a markup language much like HTML

·         XML was designed to carry data, not to display data

·         XML tags are not predefined. We must define our own tags

·         XML is designed to be self-descriptive

·         XML is a W3C Recommendation

XML allows the flexible development of user-defined document types (DTD). It provides a robust, non-proprietary, persistent, and verifiable file format for the storage and transmission of text and data both on and off the Web; and it removes the more complex options of SGML, making it easier to program for. It provides a standardized way of describing, controlling, or allowing/disallowing particular types of document structure.

 Some Important Features of XML:

     XML Separates Data from HTML

If we need to display dynamic data in our HTML document, it will take a lot of work to edit the HTML each time the data changes.

With XML, data can be stored in separate XML files. This way we can concentrate on using HTML for layout and display, and be sure that changes in the underlying data will not require any changes to the HTML.

With a few lines of JavaScript, we can read an external XML file and update the data content of our HTML.

      

XML Simplifies Data Sharing

In the real world, computer systems and databases contain data in incompatible formats.

XML data is stored in plain text format. This provides a software and hardware independent way of storing data.

This makes it much easier to create data that different applications can share.

XML Simplifies Data Transport

With XML, data can easily be exchanged between incompatible systems.

One of the most time-consuming challenges for developers is to exchange data between incompatible systems over the Internet.

Exchanging data as XML greatly reduces this complexity, since the data can be read by different incompatible applications.

XML Simplifies Platform Changes

Upgrading to new systems (hardware or software platforms), is always very time consuming. Large amounts of data must be converted and incompatible data is often lost.

XML data is stored in text format. This makes it easier to expand or upgrade to new operating systems, new applications, or new browsers, without losing data.

XML is Robust and Durable

XML provides a robust and durable format for information storage and transmission. Robust because it is based on a proven standard, and can thus be tested and verified; durable (persistent) because it uses plain-text file formats which will outlast proprietary binary ones.

XML is Used to Create New Internet Languages

A lot of new Internet languages are created with XML.

Here are some examples:

·         XHTML the latest version of HTML

·         WSDL for describing available web services

·         WAP and WML as markup languages for handheld devices

·         RSS languages for news feeds

·         RDF and OWL for describing resources and ontology

·         SMIL for describing multimedia for the web