Document Object Model

 The XML DOM (Document Object Model) defines a standard way for accessing and manipulating XML documents.  The DOM presents an XML document as a tree structure, with elements, attributes, and text as nodes.

 DOM is a standard defined by the W3C, just like XML  DOM was not designed specifically for Java technology (unlike SAX)  DOM is cross-platform and cross language  Uses OMG’s IDL to define interfaces  IDL to language binding

 Access XML document as a tree structure  Composed of mostly element nodes and text nodes  Can “walk” the tree back and forth  Larger memory requirements  Fairly heavyweight to load and store  Use it when for walking and modifying the tree

XML Document Parser Creates Tree Input

 XML document is represented as a tree  A tree is made of nodes  There are 12 different node types  Nodes may contain other nodes (depending on node types)  parent node contains child nodes

 Document node  Document Fragment node  Element node  Attribute node  Text node  Comment node  Processing instruction node  Document type node  Entity node  Entity reference node  CDATA section node  Notation node

 A document node contains  one element node (root element node)  one or more processing instruction nodes  An element node may contain  other element nodes  one or more text nodes  one or more attribute nodes  An attribute node contain  a text node

Alan Turing computer scientist

 XML Document node  element node “people”  element node “person”  element node “name”  element node “first_name” * text node “Alan” » element node “last_name” * text node “Turing”  element node “profession” » text node “computer scientist”  attribute node “born” » text node “1912”

 All modern browsers have a build-in XML parser that can be used to read and manipulate XML.  The parser reads XML into memory and converts it into an XML DOM object that can be accesses with JavaScript

xmlDoc=new ActiveXObject ("Microsoft.XMLDOM"); xmlDoc.async="false"; xmlDoc.load(“people.xml");  Code explained:  The first line creates an empty Microsoft XML document object.  The second line turns off asynchronized loading, to make sure that the parser will not continue execution of the script before the document is fully loaded.  The third line tells the parser to load an XML document called “people.xml".

Programming Interface  The DOM models XML as a set of node objects. The nodes can be accessed with JavaScript or other programming languages.  The programming interface to the DOM is defined by a set standard properties and methods.  Properties are often referred to as something that is (i.e. nodename is “name").  Methods are often referred to as something that is done (i.e. delete “name").

XML DOM Properties  These are some typical 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

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

 Accessing Nodes  You can access a node in three ways: 1. By using the getElementsByTagName() method 2. By looping through (traversing) the nodes tree. 3. By navigating the node tree, using the node relationships

 The JavaScript code to get the text from the first element in people.xml:  txt=xmlDoc.getElementsByTagName(“name")[ 0].childNodes[0].nodeValue

 After the execution of the statement, txt will hold the value “Alan" Explained:  xmlDoc - the XML DOM object created by the parser.  getElementsByTagName(“Name")[0] - the first element  childNodes[0] - the first child of the element (the text node)  nodeValue - the value of the node (the text itself)

DOM Node List Length  The length property defines the length of a node list (the number of nodes).  You can loop through a node list by using the length property: xmlDoc=loadXMLDoc(“people.xml"); x=xmlDoc.getElementsByTagName(“name"); for (i=0;i<x.length;i++) { document.write(x[i].childNodes[0].nodeValue); document.write(" "); }

Example explained:  Load “people.xml" into xmlDoc.xml  Get all element nodes  For each title element, output the value of its text node

Node Types  The documentElement property of the XML document is the root node.  The nodeName property of a node is the name of the node.  The nodeType property of a node is the type of the node.

xmlDoc=loadXMLDoc(“people.xml"); x=xmlDoc.documentElement.childNodes; for (i=0;i<x.length;i++) { if (x[i].nodeType==1) {//Process only element nodes (type 1) document.write(x[i].nodeName); document.write(" "); }

Example explained:  Load “people.xml" into xmlDoc.  Get the child nodes of the root element  For each child node, check the node type of the node. If the node type is "1" it is an element node  Output the name of the node if it is an element node

Get the Value of an Element xmlDoc=loadXMLDoc(“people.xml"); x=xmlDoc.getElementsByTagName("title")[0].c hildNodes[0]; txt=x.nodeValue; x.nodeValue=“charles";

The nodeType Property  The nodeType property specifies the type of node.  nodeType is read only.  The most important node types are: