Understanding XML DOM

Understanding
XML DOM
(W3C Standard)

Created by :
Om Vikram Thapa

INDEX :
 XML DOM – Introduction
 DOM Nodes (Tree Structure)
 DOM Parsing
 DOM Load Functions (in IE & FireFox)
 DOM Properties & Methods
 DOM HttpRequest
 DOM Node Types
 DOM Parse Error Objects
 Thank You!!

XML DOM (INTRODUCTION)
 The XML DOM (Document Object Model) defines a standard
way for accessing and manipulating XML documents.

 The DOM is a W3C (World Wide Web Consortium) standard.

 DOM defines the objects and properties and methods (interface)
to access all XML elements.

 The DOM presents an XML document as a tree structure, with
elements, attributes, and text as nodes.

 The DOM is separated into 3 different parts / levels:
Core DOM - standard model for any structured document
XML DOM - standard model for XML documents
HTML DOM - standard model for HTML documents

What is an XML DOM?
 The XML DOM is:
- A standard object model for XML
- A standard programming interface for XML
- Platform and language-independent
- A W3C standard
 The XML DOM defines the objects and properties
of all XML elements, and the methods (interface) to
access them.
 The XML DOM is a standard for how to get, change,
add or delete XML elements.

AN EXAMPLE OF books.xml:
<bookstore>
- <book category="cooking">
<title lang="en">Italian</title>
<author>Giada De Laurentiis</author>
<year>2005</year>
<price>30.00</price>
</book>
- <book category="language">
<title lang="en">English</title>
<author>Om Vikram</author>
<year>2005</year>
<price>50.00</price>
</book>
</bookstore>

DOM NODES DESCRIPTION
 According to the DOM, everything in an XML
document is a node.
 The entire document is a document node .
 Every XML element is an element node .
 The text in the XML elements are text nodes .
 Every attribute is an attribute node .
 Comments are comment nodes.
In our ex.
- The root node <bookstore> holds four <book> nodes.
- Each <book> node contain 4 text node i.e.
<title>, <author>, <year>, and <price>

XML DOM PARSING:
 Most browsers have a build-in XML parser to read
and manipulate XML.
 The parser reads XML into memory and converts
XML it into XML DOM object which is accessible
from JavaScript .
 There are some differences between Microsoft's
XML parser and the parsers used in other browsers.
 The MS parser supports loading of both XML files
and XML strings (text)
 Other browsers use Separate parsers.
 However, all parsers contain functions to traverse
XML trees, access, insert, and delete nodes.

Loading XML with IE using MS
XML Parser:
 The following JavaScript fragment loads an XML
document “book.xml” into the parser :
xmlDoc=new ActiveXObject("Microsoft.XMLDOM");
xmlDoc.async="false";
xmlDoc.load("books.xml");

 The following JavaScript fragment loads an XML text
into the parser :
xmlDoc=new ActiveXObject("Microsoft.XMLDOM");
xmlDoc.loadXML(txt);

Loading XML with FireFox & Other
XML Parser :
 The following JavaScript fragment loads an XML
document “book.xml” into the parser :

xmlDoc=document.implementation.createDocument("","",null)
;
xmlDoc.load("books.xml");

 The following JavaScript fragment loads an XML text
into the parser :
parser=new DOMParser();
xmlDoc=parser.parseFromString(txt,"text/xml");

DOM PROPERTIES & METHODS:
 XML DOM Properties:
 x.nodeName - the name of x
 x.nodeValue - the value of x
 x.parentNode - the parent node of x
 x.childNodes - the child nodes of x
 x.attributes - the attributes nodes of x
(where x is a node object. )
 XML DOM Methods:
 x.getElementsByTagName(name) - get all elements
with a specified tag name
 x.appendChild(node) - insert a child node to x
 x.removeChild(node) - remove a child node from x

AN EXAMPLE :
txt=xmlObj.getElementsByTagName("title")[0].childNodes[0].nodeValue;

where
 xmlObj - the XML DOM object created by the parser.
 getElementsByTagName("title")[0] - the first <title>
element
 childNodes[0] - the first child of the <title> element (the
text node)
 nodeValue - the value of the node (the text itself)

NODE TYPES
NodeTypes Named Constants
 1 ELEMENT_NODE
 2 ATTRIBUTE_NODE
 3 TEXT_NODE
 4 CDATA_SECTION_NODE
 5 ENTITY_REFERENCE_NODE
 6 ENTITY_NODE
 7 PROCESSING_INSTRUCTION_NODE
 8 COMMENT_NODE
 9 DOCUMENT_NODE
 10 DOCUMENT_TYPE_NODE
 11 DOCUMENT_FRAGMENT_NODE
 12 NOTATION_NODE

DOM PARSE ERROR OBJECTS
 When trying to open an XML document, a parser-error may
occur.
 With the parseError object, you can retrieve the error code, the
error text, the line that caused the error, and more.
Property Description
 errorCode Returns a long integer error code
 Reason Returns a string containing the reason for the error
 Line Returns a long integer representing the line
number for the error
 Linepos Returns a long integer representing the line
position for the error
 srcText Returns a string containing the line that caused the
error
 url Returns the URL pointing the loaded document
 Filepos Returns a long integer file position of the error

Understanding XML DOM

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