evolution of DOM



                                                                Evolution of DOM
The document object model (DOM) is a cross-platform and language-independent convention for representing and interacting with object in HTML, XML,XHTML,and XML document. The nodes of every document are organized as tree structure, called the DOM tree.
Object in Dom tree may be addressed and manipulated by using method on object. The public interface of DOM is specify in his its application programing interface (API)


 The history of DOM:-
The history of the document object model is intertwined with the history of the ‘brows wars ‘of the the late 1990 between Netscape Navigator and Microsoft Internet Explorer, as well as with that of JavaScript and jscript  the first scripting language to be  widely implemented in the layout engine of web browsers.
Structure of DOM:-


Tree Structure of DOM:-




Working Diagram:-



Legacy DOM:-

JavaScript was released by Netscape communication in 1995 within Netscape navigator 2.0.Netscap’caompetitor, Microsoft released internet explorer3.0 the following year with a port of JavaScript called jscript.
Legacy DOM was limited in the kinds of element that could be accessed. The legacy DOM enabled client-side validation form validation and “rollover” effect.

Intermediate DOM:-

In 1997, Netscape and Microsoft released version 4.0 of Netscape Navigator and intent explore respectively, adding support for dynamic HTML(Dhtml),functionality enabling changes to a loaded HTML document.DHTML requires extension to the rudimentary document object that was available in the the legacy DOM imlementations.although the legacy DOM implementation were developed in parallel by each Browser maker and remained incompatible. These versions of the Dom become known as the “intermediate DOM”.

Standardization:-

Level1-

The initial DOM standard, known as “DOM level1,”was recommended by W3C in late 1998, it provide a complete model of an entire HTML or XML document.
Level2-

DOM Level2 was published in late 2000.it introduced the “getElmentByld”function as well as an m event model and support for XML namespaces and CSS.
Level-3
DOM Level3,the current release of the the DOM specification, published in April 2004,added support for Xpath and keyboard event handling, as well as an interface for serializing document as XML

Level4-

DOM Level4 is currently being developed. Last call working draft was released in February 2014

Applications:-

Browser:-

To render a document such as HTML page, most Web Browsers an internal model similar to the DOM.
The nodes of every document are organized in a tree structure, called the DOM tree, with topmost node named document object when an html page is rendered in browsers.
The browser downloads the HTML into local memory and automatically parses it to display the page on screen. The DOM is also the way JavaScript transmit the state of the browser in HTML pages.

Implementation:-

Because DOM support navigation in any direction (eg parent and previous sibling) and allows for arbitrary modifications, an implementation must at least buffer the document that has been read so far(or some parsed from of it)

Library:-
DOM implementations:-
1-Libxml2
2-MSXML
3-Xerces  is a collection of DOM implementation written in c++.java and perl
4-XML for <script> is a JavaScript-based DOM implementation
5-API that expose DOM implementations
6-AJAXP (java API for XML processing) is an API for accessing DOM providers
7-Lazarus(free Pascal IDE) contains two variant of the DOM-q\with UTF-8 and ANSI format inspection tools
8-DOM inspector is a web developer tool

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