Introduction to the Document Object Model

Eugenia FernandezIUPUI

Document Object Model (DOM)

XML DOM is an object model that exposes the contents of an XML document. Exposed means that the content of the

document can be accessed and manipulated – via programs or scripts.

The DOM defines a set of objects that allow the nodes of an XML document tree to be accessed and modified.

DOM NodesNode Description

Node Any document component such as an element, attribute, comments or text string

Document The entire document, comprising all nodes

Element A document element

Attr An attribute of an element as a name/value pair

Processing Any processing instruction encoded in the document

Instruction Comments, ignored by the parser

Text Text content of an element

The DOM Tree Structure Recall that an XML

parser takes an XML document and creates a tree structure to represent the document.

The tree structure shows the hierarchy of data in the XML document.

DOCUMENT

DocumentElement

Element

Attr

Text

Element

Text

Text

Everything is a Node Every ‘branch’ of the XML DOM tree is a Node object.

Common Node methods firstChild, lastChild, nextSibling,

previousSibling Common Node properties

nodeValue nodeType nodeName

Node nodeType value

Document NODE_DOCUMENT

Element NODE_ELEMENT

Attr NODE_ATTRIBUTE

Text NODE_TEXT

Example

The entire XML document is a Document node, <order> and <orderitem> are Element nodes, title and isbn are Attr nodes, and the values “XML by Example” and “12345675” are Text nodes.

<xml>

<order> <orderitem title=“XML by Example” isbn=“12345675”/> </order>

</xml>

Create the Document Object: Version 1

From XML data island

The XMLDocument property of the data island provides a reference to the Document object

<XML id=“booksdso” src=“books.xml”></XML>

Set doc = booksdso.XMLDocument

Create the Document Object: Version 2

From external XML file create a DOM document using the CreateObject method set the async property to False to indicate NOT to load the

XML file asynchronously, if loaded async, the parser halts execution until the entire document is loaded

load the XML file into the Document object

alternatively, you can load an XML string instead of a file

Set doc = CreateObject(“Microsoft.XMLDOM”)

[or set doc = CreateObject(“MSXML2.DOMDocument”)]

doc.async = False

doc.load “Books.xml”

doc.load “<?xml version=‘1.0’?><booklist></booklist>”

Accessing Nodes Within a DOM object, once you access a

particular node you can use its properties/methods to determine its location in the document tree child nodes parent node siblings and ancestors attributes

Accessing the root element set rootNode = doc.documentElement

Node Properties & Methods nodeType, nodeName, nodeValue parentNode

parent node, if any childNode

set of child nodes firstChild, lastChild previousSibling, nextSibling attributes

set of attributes of the current node, if any

Navigating Elements

DOCUMENT

theNode

theNode.parentNode.lastChild

theNode.parentNode.childNodes(0)

theNode.parentNode

theNode.ownerDocument

theNode.nextSibling

Collections Each node potentially has a

collection, or set, of child nodes. Collections have methods used to

traverse the nodes sequentially. Numbering starts at 0.

Navigating Node Collections childNodes property returns a NodeList

object – a zero-based collection of nodesset doc = booksdso.XMLDocumentset rootnode = doc.documentElementfor each child in rootNode.childNodes ‘process data in child nodenext

‘orset children = rootNode.childNodesfor I=0 to children.length-1 ‘process data in children.item(I)Next

Retrieving Node Content nodeType

type of node expressed by number• 9 = document node• 1 = element node• 2 = attribute node

nodeName name of the node

Retrieving a Node’s Value nodeValue

value of a text node or attribute node The nodeValue of an element is null.

Its text is held in a child text node. To retrieve its value, you must retrieve the value of first child.

<book title=“XML by Example”>

set title = rootNode.firstChild.childNodes(0)set titleValue = title.firstChild.nodeValue

The Document Object The topmost node in a DOM tree (NOT the

root XML element, but above that – represents the entire document)

This is set by the creation of the DOM tree (either version 1 or version 2).

Has two properties: documentElement

• this is the root element of the XML document• accessed as doc.documentElement

doctype• not specified in DOM level 1

The Element Object Represents XML elements Adds new property:

tagName Adds new method

getElementByTagName() • returns a node set of all descendants of the

element with a given tag name

Accessing Attributes Use the attributes property to

access the value of attributes Example

This retrieves the value of the first attribute of the first child node of the root element (doc.documentElement)

doc.documentElement.firstChild.attributes(0).value

Microsoft Extensions nodeTypeString

type of node expressed as a string, e.g. “document”, “element”, “attribute”

text returns text content of the node and all

its descendants xml

returns XML of the node and all its descendants

Viewing XML Data Microsoft’s DOM defines an xml

property in the Node object. This allows you to retrieve the XML data contained in that portion of the tree, i.e. the subtree that starts at the selected node.

Msgbox booksdso.XMLDocument.xmlMsgbox booksdso.XMLDocument.document element.xml

Source “Building XML-Based Web

Applications” a Microsoft Certified Course.