XML Tutorial The What, The When, The Where, The Why and The How

Author: Jaidev

What is this thing?

XML is an acronym for eXtensible Markup Language.
As the name suggests it is yet another language specification. But a very special one at that. And till extra sensory perception becomes commonplace, we all need languages to communicate, don’t we?

When and Where did it happen?

Before the child there was the mother.

* 1986. International Standards Organization.

SGML is born. SGML or the Standard Generalized Markup Language made it possible to present the same electronic text the same useful way irrespective of producer or consumer. In more technical words, SGML is a global standard for the definition of device- and system-independent methods of representing electronic text. And then the web revolution happened.

* 1996. World Wide Web Consortium.

XML is born. This child is well adapted to the web environment. And while its elder sibling Hypertext Markup Language (HTML) looks good, this one has great depth in meaning. Well, almost as much depth as one would like it to have.

Why do we need it?

So why did evolution take us down the XML path? This is because XML took us beyond mere presentation of information and into the realm of representation of information. No longer was this content just a mass of data to be rendered solely for viewing on a browser. Now the content could be structured and the meaning attached to this structure could be transmitted as well. So the lifeless data is suddenly transformed into a live and fundamentally more useful form. Today people use XML for information transfer across platforms, devices and communication channels irrespective of how these actually work beneath. Whether you have an internet web browser, a GSM handphone browser, a dedicated kiosk or an over the cable interactive TV console, you can have access to the data all the same. Whether you have a database, a text file or you own proprietary format for storing information (anything but ink on physical papyrus paper!) your applications can share content.

How does this magic take place?

Actually, there is neither magic nor any rocket science here. The power of XML is actually hidden in the meaning of the first two key words that constitute the acronym XML itself. Let us consider these. Extensible: The XML language is extensible. Basically what this means is that if one has defined a name as First Name and Last Name You can step in and extend the definition to Salutation, First Name, Middle Name and Last Name Thus the definition of name is no longer stationary, but can actually evolve according to the times and the needs. * Advantage? Very easy to refine and redefine concepts. Avoid definition lock-ins. * Disadvantage? Well there is a downside but it is minor and we will discuss that in a later chapter. Meanwhile, take a logical shot! Markup: Everything is expressed as markup in XML. For instance, a simple XML version of a name could be: What you see in angled brackets <> is the markup also called tags by many. They express the meaning of the content they enclose. * Advantage? If you understand what the markup actually means, you can use the data very productively. For instance if you knew that a salutation of “Dr.” implies the person holds a Doctorate, you may want to place a special reservation on the researchers dinner table. * Disadvantage? None–well almost. But again, we will come to that in a later chapter. Meanwhile, take a logical guess again!

Moving on

In this chapter we were initiated. Now that we have entered the gates, let us venture back XML memory lane and understand its origins in some detail. We shall see the need for electronic document standardization and how that need has changed with time and technology. We will focus on SGML, HTML and finally on XML itself, understanding the role of each and the relationships between them.