Since its evolution, the HTML (Hyper Text Markup Language) has been revised and upgraded a number of times in order to make the World Wide Web a better place to live virtually. HTML is a derivative of SGML (Standard Generalized Markup Language), but its major flaw is that it is not extensible. Thus HTML is not appropriate for deployment under a network environment.
So, the World Wide Web Consortium (popularly known as W3C) decided to develop a new breed of extensible language and came up with XML, which stands for eXtensible Markup Language. Web developers use XML to dynamically describe the information stored on a web page. Though XML, the new generation web pages describes themselves which is helpful to gain good rankings in search engine listings and help the developers to write codes for custom search tools.
• XML shall be straightforwardly usable over the Internet.
• XML shall support a wide variety of applications.
• XML shall be compatible with SGML.
• It shall be easy to write programs that process XML documents.
• The number of optional features shall be kept to the absolute minimum, ideally zero.
• XML documents shall be human-legible and reasonably clear.
• The XML design should be prepared quickly.
• The design of XML shall be formal and concise.
• XML documents shall be easy to create.
• Terseness in XML markup is of minimal importance.
(Source: http://www.w3.org/TR/REC-xml/)
XML is referred as a Metalanguage which describes other languages. It is called so because XML allows the web developers to create documents which describes themselves to their reader. Though the XML tags look like the HTML ones, the main difference between the two is that the HTML documents do not tell the web browser how to display the web page. On the other hand, the XML documents are downloaded by the web browser along with a style sheet or Document Type definition (DTD) which guides the web browser on how to display the web page.
In its raw form, an XML document looks like the HTML and SGML documents, but all are functionally different. The main difference between the HTML and XML coding is that the XML tags are very rigid. For example; the HTML language has tags which have a closing and which don’t have a closing section. But in XML either all the tags must exist in pair or announce to the reader that a closing tag is not present.
For example: in HTML you can use <BR> tag without having to close it, but in XML you have to use it as <BR>…</BR> or simply as <BR/> which announces that there is no closing tag for BR.
Another prominent difference between the two languages is that the XML requires all the tag attribute values to be enclosed within quotation marks. For example:
<font color=red>……</font>, this is wrong in XML. It should be like <font color=”red”>…….</font>
HTML is used to create and design static web pages. It proved to be very useful and easy to understand and soon after its evolution it gained world wide popularity rapidly. But with the growth of internet and its related applications the internet users demanded something more in the websites. Web surfers were vigorously expecting more interactive, entertaining and exciting web content. Thus DHTML was introduced. Some people call DHTML as an advanced version of HTML, but some did not consider it a language or a new specification of HTML. Rather, they perceive DHTML as a new way of controlling the HTML commands and functions. DHTML is basically an amalgamation of four different techniques i.e. HTML, Scripting, Cascading Style Sheets (CSS) and Document Object Model (DOM). Using all these tools we can create more interactive and animated web pages to arrest the attention of the internet users. DHTML is used to insert special effects to a website such as mouse rollover effects, drop down lists, animations, advanced marquee effects etc. It allows you to control the HTML elements and change them.
The four techniques which are harmonically used in DHTML are:
1) HTML: DHTML uses the standard HTML code as its base.
2) Scripting: A client side scripting language such as Java Script is used to control the elements in DHTML
3) CSS: Cascading Style Sheets are also used to define and manage the style and layout of the web pages.
4) DOM: Document Object Model allows you to access any portion of a DHTML document and change its properties.
DHTML adds life to static HTML pages. The user feels that he is interacting with the website in real time. DHTML can add an effect with any event. For example when you click on an image, it background changes. In this the effect is related with the mouse click event. Similarly a lot of events such as mouse rollover, drag n drop, scroll etc. can be associated with one or more DHTML effects.
The four properties of DHTML are:
1) DHTML is used to modify and control the standard HTML tags and their attributes.
2) DHTML gives you real time interactivity with the web page. It can position different objects, images and text dynamically within the web page.
3) DHTML is also used dynamic fonts. Only Netscape Navigator supports this function.
4) Another important feature of DHTML is Data Binding. With the help of this property the web surfer can easily access databases from the websites. This feature is only supported by Microsoft’s Internet Explorer.
It is clear from the above discussion that DHTML has many advantages and some disadvantages too. DHTML is more complex than HTML. The DHTML editors are very costly. Apart from this some of the features of DHTML are browser specific but still DHTML is used worldwide as it has proved itself a great utility to enhance the quality and usability of web pages. Anyone can use DHTML in any form. From a small piece of creativity to large complex codes, DHTML can be used to make web sites better than ever before.
