How Can XML be Used?

XML is used in many aspects of web development, often to simplify data storage and sharing.
XML Separates Data from HTML

If you need to display dynamic data in your 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 you 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, you can read an external XML file and update the data content of your HTML.

You will learn more about this in a later chapter of this tutorial.
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 Makes Your Data More Available

Since XML is independent of hardware, software and application, XML can make your data more available and useful.

Different applications can access your data, not only in HTML pages, but also from XML data sources.

With XML, your data can be available to all kinds of "reading machines" (Handheld computers, voice machines, news feeds, etc), and make it more available for blind people, or people with other disabilities.
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

If Developers Have Sense

If they DO have sense, future applications will exchange their data in XML.

The future might give us word processors, spreadsheet applications and databases that can read each other's data in a pure text format, without any conversion utilities in between.

We can only pray that all the software vendors will agree.

Introduction to XML

XML was designed to transport and store data.

HTML was designed to display data.
What You Should Already Know

Before you continue you should have a basic understanding of the following:

* HTML
* JavaScript

If you want to study these subjects first, find the tutorials on our Home page.
What is 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. You must define your own tags
* XML is designed to be self-descriptive
* XML is a W3C Recommendation

The Difference Between XML and HTML

XML is not a replacement for HTML.
XML and HTML were designed with different goals:

XML was designed to transport and store data, with focus on what data is.
HTML was designed to display data, with focus on how data looks.

HTML is about displaying information, while XML is about carrying information.
XML Does not DO Anything

Maybe it is a little hard to understand, but XML does not DO anything. XML was created to structure, store, and transport information.

The following example is a note to Tove from Jani, stored as XML:
<note&rt;
<to&rt;Tove</to&rt;
<from&rt;Jani</from&rt;
<heading&rt;Reminder</heading&rt;
<body&rt;Don't forget me this weekend!</body&rt;
</note&rt;

The note above is quite self descriptive. It has sender and receiver information, it also has a heading and a message body.

But still, this XML document does not DO anything. It is just pure information wrapped in tags. Someone must write a piece of software to send, receive or display it.
XML is Just Plain Text

XML is nothing special. It is just plain text. Software that can handle plain text can also handle XML.

However, XML-aware applications can handle the XML tags specially. The functional meaning of the tags depends on the nature of the application.
With XML You Invent Your Own Tags

The tags in the example above (like <to&rt; and <from&rt;) are not defined in any XML standard. These tags are "invented" by the author of the XML document.

That is because the XML language has no predefined tags.

The tags used in HTML (and the structure of HTML) are predefined. HTML documents can only use tags defined in the HTML standard (like <p&rt;, <h1&rt;, etc.).

XML allows the author to define his own tags and his own document structure.
XML is Not a Replacement for HTML

XML is a complement to HTML.

It is important to understand that XML is not a replacement for HTML. In most web applications, XML is used to transport data, while HTML is used to format and display the data.

My best description of XML is this:

XML is a software and hardware independent tool for carrying information.
XML is a W3C Recommendation

The Extensible Markup Language (XML) became a W3C Recommendation 10. February 1998.
XML is Everywhere

We have been participating in XML development since its creation. It has been amazing to see how quickly the XML standard has developed and how quickly a large number of software vendors have adopted the standard.

XML is now as important for the Web as HTML was to the foundation of the Web.

XML is everywhere. It is the most common tool for data transmissions between all sorts of applications, and becomes more and more popular in the area of storing and describing information.

Next

XML Tutorial

XML stands for EXtensible Markup Language.

XML was designed to transport and store data.

In this tutorial you will learn about XML, and the difference between XML and HTML.

XML is important to know, and very easy to learn.

Start learning XML!