1. Introduction to the Document Object Model
Eugenia Fernandez
IUPUI

2. 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.

3. DOM Nodes Node Description
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

4. 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
Document
Element
Element
Attr
Text
Text
Element
Text

5. 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

6. Example
<xml>
<order> <orderitem title=“XML by Example” isbn=“ ”/> </order>
</xml>
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 “ ” are Text nodes.

7. 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

8. 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>”

9. 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

10. 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

11. Navigating Elements DOCUMENT theNode theNode.ownerDocument
theNode.parentNode
theNode.parentNode.childNodes(0)
theNode
theNode.nextSibling
theNode.parentNode.lastChild

12. 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.

13. Navigating Node Collections
childNodes property returns a NodeList object – a zero-based collection of nodes
set doc = booksdso.XMLDocument
set rootnode = doc.documentElement
for each child in rootNode.childNodes
‘process data in child node
next
‘or
set children = rootNode.childNodes
for I=0 to children.length-1
‘process data in children.item(I)
Next

14. Retrieving Node Content
nodeType
type of node expressed by number
9 = document node
1 = element node
2 = attribute node
nodeName
name of the node

15. 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

16. 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

17. 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

18. 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

19. Microsoft Extensions nodeTypeString text xml
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

20. 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.xml
Msgbox booksdso.XMLDocument.document element.xml

21. Source
“Building XML-Based Web Applications” a Microsoft Certified Course.