WORKING WITH THE DOCUMENT OBJECT MODEL

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New Perspectives on XML, 2nd EditionTutorial 10

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WORKING WITH THE DOCUMENT OBJECT MODEL

TUTORIAL 10

XPUpdating XML documents


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XPXML API

• XML and XSLT are a markup languages– Describe how things are arranged and how things look

• API– Collection of prewritten procedures

– Enables processing of XML

• Two APIs for use with XML– W3C DOM (Document Object Model)

• Requires entire XML document be held in memory; memory intensive

– SAX (Simple API for XML)• Can be used on a stream of XML which need not be held entirely in memory

• Developed by XML-DEV mailing list


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DOM LEVELSPage 572

XPGeneral approach

1. Determine which browser is being used

2. Create document object

3. Load a file into the document object

4. Transform the document object using XSLT

5. Display the transformed document


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CREATING A CROSS-BROWSER SOLUTION

• Because there are some fundamental differences between Internet Explorer and the Mozilla-based browsers in implementing the Document Object Model, any program code that you write has to first determine which browser is in use.– Object-detection

<script type=“text/javascript”>

var IE = window.ActiveXObject ? true:false;

var MOZ = document.implementation.createDocument ? true:false;

</script>

Java Script is case sensitive

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CREATING A CROSS-BROWSER SOLUTION

if (IE) {

Internet Explorer code

} else if (MOZ) {

Mozilla code

}

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CREATING A DOCUMENT OBJECT IN INTERNET EXPLORER

• A document object is an object that can store the contents and structure of a document.

docObj = new ActiveXObject(PID);

– docObj is the variable name of the document object– PID is the program ID that indicates the type of

document object to be created.

Each version of MSXML supports a different program ID

XPCREATING A DOCUMENT OBJECT IN INTERNET EXPLORER

• IE creates document objects using ActiveX– Microsoft technology used to create interactive content for the web

• Program IDs supported by different versions of MSXMLMsxml2.DOMDocument.5.0

Msxml2.DOMDocument.4.0

Msxml2.DOMDocument.3.0

MSXML2.DOMDocument

Microsoft.XMLDOM

• Example:XMLdoc = new ActiveXobject

(“Msxml2.DOMDocument.3.0”);New Perspectives on XML, 2nd Edition

Tutorial 1010

To determine the most recent version, query the browser

(page 576)

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CREATING A DOCUMENT OBJECT IN MOZILLA

• SyntaxdocObj = document.implementation.createDocument

(uri,root,doctype);uri is the URI of the document’s namespace

root is the qualified name of the document’s root element

doctype is the type of document to create (always enter a value of null)

• ExampleXMLdoc = document.implementaton.createDocument

(“http://lhouse.org”, Persons, null);

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LOADING A FILE INTO A DOCUMENT OBJECT

• First choose load strategy:– An asynchronous load does not require the application loading

the file to wait for it to finish loading before proceeding through the lines in the program code

– A synchronous load causes the application to stop until the file is completely loaded.

• Example: choose synchronous loaddocObj.async=false;

• Example load:docObj.load(url)

Default

Use for large files or retrieving files

through a slow internet connection

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Transforming a Document Using XSLT

(Internet Explorer)

• Because XSLT style sheets are also XML documents, you need to create a document object using ActiveX for the style sheet– Rental-threaded model

• Content is accessed by the XML processor using a single sequence of instructions

– Free-threaded model• Content is access by the processor through multiple input

threads

Preferable for efficiency reasons

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Transforming a Document Using XSLT

(Internet Explorer)

• Once a style sheet is loaded, IE applies the style sheet to the source document using either of two methods:– transformNode()

• Creates a text string containing the code for the result document

– transformNotetoObject()• Stores the result lin another

document object

• Either method can be drag on resources– Create a template Object and Processor Object…

Simple

Can write code to further

manipulate the contents

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Template and Processor Objects (Internet Explorer)

• Template object– Uses a large and complicated style sheet or for programs that need

to run several transformations,

– Increases the efficiency of the program because the cached style sheet can be accessed repeatedly without being recompiled

• Processor object– Processes the template object to produce the result object

• Display the result object

XPCreating a Template Object (Internet Explorer)

• Processor must compile the style sheet object each time the transformation is run.

• For large and complicated style sheets or programs that need to run several transformations, store the style sheet in a template object and use the free-threaded model

• Store the program IDs in an array:Var FreeThreadPID = [“Msxm1.FreeThreadedDocument.5.0”,

“Msxm1.FreeThreadedDocument.4.0”, “Msxm1.FreeThreadedDocument.3.0”];

• Create document object for the style sheetXSLTdoc=New Active Xobject

(getPID (FreeThreadPID) );


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XPUsing a processor object (Internet Explorer)

• Steps for creating and using a processor object1. Insert a free-threaded style sheet into the template object

2. Create an XSLT processor based on the template

3. Specify an input source document for the processor

4. Transform the source document based on the style sheet

Examplefunction doTransform() {

var contTable = document.getElementById(“ctabale”)”

If (IE) {

XSLTemp.stylesheet=XSLTdoc:

XSLTProc=XSLTemp.createprocessor();

XSLTProc.input=XMLdoc;

XSLTLProc.transform()XSLTproc.out;

}

}

See pages 584-587 for detailsNew Perspectives on XML, 2nd Edition

Tutorial 1019

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TRANSFORMING A DOCUMENT WITH MOZILLA

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TRANSFORMING A DOCUMENT WITH MOZILLA

Figure 10-17 page 589

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CONVERTING A DOCUMENT OBJECT OR FRAGMENT TO A TEXT STRING

WITH MOZILLA

• To convert a document object or a fragment to a text string in Mozilla, you create a serializer object, which contains a textual representation of the contents of a document object or fragment

serialObj = new XMLSerializer();Where serialObj is the serializer object that will contain the text of the document object or fragment.

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CONVERTING A DOCUMENT OBJECT OR FRAGMENT TO A TEXT STRING

WITH MOZILLAFigure 10-18 Page 591

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• Display the document:


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WORKING WITH THE DOCUMENT OBJECT

Page 592

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WORKING WITH THE DOCUMENT OBJECT

Page 593

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VIEWING THE NODE TREE

• A node that contains other nodes is a parent node, and the

• nodes it contains are child nodes.

• Nodes that share the same parent are sibling nodes.

• Nodes can contain different types of content. For example, element nodes refer to elements from the Document Object Model, and text nodes refer to the actual text content of element nodes.

• Attribute nodes refer to the attributes contained within elements or processing instructions.

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ACCESSING ELEMENTS BY TAG NAME

docObj.getElementsByTagName(tag)

Where docObj is the document object and tag is the element’s tag name.

Example:XMLdoc.getElementsByTagName("person")

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USING FAMILIAL RELATIONS

• Each node in a node tree can also be treated as a node object with its own collection of properties and methods

nodeObj.firstChild

Where nodeObj is a node from the document’s node tree.

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USING FAMILIAL RELATIONSPage 595

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NODE TYPES, NAMES, AND VALUES

• nodeObj.nodeType• nodeObj.nodeName• nodeObj.nodeValue

Page 596

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ADDING AND REMOVING NODES

nodeObj = docObj.createElement(tag);

Where– nodeObj is the new element node

– docObj is the document object containing the new node

– tag is the tag name associated with the element

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CREATING NODE OBJECTS

Page 599

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INSERTING AND REMOVING NODES

Page 600

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CREATING A DOCUMENT FRAGMENT

Page 601

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CLONING A DOCUMENT FRAGMENT Page 602

XPAdd new Records to the Contribution List


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ATTRIBUTE METHODSPage 609

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FILTERING THE SOURCE DOCUMENT

<xsl:param name="group" select="//person" />

<xsl:param name="group" select="//person[amount > 100]" />

Page 614

XPFILTERING THE SOURCE DOCUMENT

function filterList() {

var filterStr = document.webform.filter.value;

if (filterStr==“”) filter=“//person”

else filter = “//person[“+filterStr+”]”;

}


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Extract filter expression from formInsert filter expression

into parameter

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SETTING A PARAMETER VALUEin Internet Explorer

processorObj.addParameter(parameter, value, uri)

• processorObj is a processor object • parameter is the name of the style sheet parameter• value is the value passed to the parameter• uri is an optional value that specifies the

namespace URI for the parameter

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SELECTING A NODE SETin Internet Explorer

object.selectSingleNode(xpath)

Where object is a document or node object and xpath is an XPath expression.

object.selectNodes(xpath)

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SAVING AN XML DOCUMENT

docObj.save(location)

Where location is one of the following:– A filename

– The name of another document object

– An ASP (Active Server Pages) response object

– A custom COM object that supports persistence

• Supported on IE on a Web server.

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WORKING WITH AJAX

• AJAX, or Asynchronous JavaScript and XML, refers to the use of HTML, XML, XSLT, and JavaScript to enable fast, efficient communication between applications running on a user’s browser and data stored and updated on a secure Web server.

• In the classic Web application model, a user interacts with a Web server through a Web page running on their browser.

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WORKING WITH AJAX

• The AJAX Web application model adds an intermediary between the user and the server-side system, which is called an AJAX engine.

• The AJAX engine is responsible for communicating with the server and for relaying any information from the server to the user interface.

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WORKING WITH AJAX

Ajax engine:• Written in JavaScript• Ajax uses HTTP to communicate with Web server• Client uses JavaScript call functions to communicate with Ajax engine• Ajax engine placed within Web page• Enables asynchronous rather than synchronous communication

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WORKING WITH AJAXPage 628

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THE XMLHttpRequest OBJECT

• Internet Explorer– To create an XMLHttpRequest object, use

reqObj = new ActiveXObject(progID);

Where reqObj is the XMLHttpRequest object and progID is an ActiveX program ID for XMLHttpRequest objects.

• Mozilla and Safari– To create an XMLHttpRequest object, use

reqObj = new XMLHttpRequest();

Ajax engine

Ajax engine

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METHODS OF THE XMLHttpRequest OBJECT

Page 630

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PROPERTIES OF THE XMLHttpRequest OBJECT

Page 631

Documents

WORKING WITH THE DOCUMENT OBJECT MODEL