Introduction to the Document Object Model Eugenia Fernandez IUPUI

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 Nodes NodeDescription NodeAny document component such as an element, attribute, comments or text string DocumentThe entire document, comprising all nodes ElementA document element AttrAn attribute of an element as a name/value pair ProcessingAny processing instruction encoded in the document InstructionComments, ignored by the parser TextText 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 Document Element Attr Text Element 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 NodenodeType value DocumentNODE_DOCUMENT ElementNODE_ELEMENT AttrNODE_ATTRIBUTE TextNODE_TEXT

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

Create the Document Object: Version 1 From XML data island The XMLDocument property of the data island provides a reference to the Document object 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 “ ”

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 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

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

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