XML

XML Tutorial
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XML stands for EXtensible Markup Language.

XML was designed to transport and store data.

In this tutorial you will learn about XML, and the difference between XML and HTML.

XML is important to know, and very easy to learn.

Start learning XML now!

Table of Contents

Introduction to XML
What is XML, and how does it differ from HTML?

How XML can be used
Some of the different ways XML can be used.

XML Tree
How an XML document forms a logical tree structure.

XML Syntax
The logical and very simple syntax rules of XML.

XML Elements
XML Elements, naming rules, and their parent and child relationships.

XML Attributes
How attributes can be used to provide additional information about elements.

XML Validation
The difference between a well-formed and a valid XML document, and how to specify the structure of an XML document.

XML Validator
A simple on-line tool for syntax-checking (validating) XML.

Viewing XML in Browsers
How to view XML files with your browser.

Displaying XML with CSS
How to use CSS to display an XML file.

Displaying XML with XSLT
How to use XSLT to display an XML file.
XML JavaScript

XML Parser
How to use your browser to read, update, create, and manipulate XML documents.

XML DOM
About XML Document Object Model (The DOM).

XML to HTML
How to display XML data inside HTML documents.

XML HTTP Requests
How to update a page with data from a server without reloading the page (AJAX).

XML Applications
How to use XML data and JavaScript to create a complete HTML application.
XML Advanced

XML Namespaces
How XML namespaces can be used to avoid element name conflicts.

XML CDATA
How store invalid XML data inside a valid XML document.

XML Encoding
How to use different character sets in your XML documents.

XML Server
How to output XML from the server.

XML DOM Advanced
More about XML Document Object Model (The DOM).

XML Don’t
This chapter describes some technologies you should try to avoid when using XML.

XML Technologies
The most common XML-related languages.

XML in Real Life
Real-life examples of how XML can be used.

XML Editors
Why you should use an XML editor when you edit your XML documents.

XML Summary
This chapter contains a summary on what you have learned in this tutorial and a recommendation on what to do next.
XML Examples

Learn by examples! With our editor, you can edit XML and click on a test button to view the result.

Try-It-Yourself!
XML Quiz Test

Test your XML skills at W3Schools!

Start the XML Quiz!

XML was designed to transport and store data.

HTML was designed to display data.
What You Should Already Know

Before you continue you should have a basic understanding of the following:

* HTML
* JavaScript

If you want to study these subjects first, find the tutorials on our Home page.
What is XML?

* XML stands for EXtensible Markup Language
* XML is a markup language much like HTML
* XML was designed to carry data, not to display data
* XML tags are not predefined. You must define your own tags
* XML is designed to be self-descriptive
* XML is a W3C Recommendation

The Difference Between XML and HTML

XML is not a replacement for HTML.
XML and HTML were designed with different goals:

XML was designed to transport and store data, with focus on what data is.
HTML was designed to display data, with focus on how data looks.

HTML is about displaying information, while XML is about carrying information.
XML Does not DO Anything

Maybe it is a little hard to understand, but XML does not DO anything. XML was created to structure, store, and transport information.

The following example is a note to Tove from Jani, stored as XML:

Tove
Jani
Reminder
Don’t forget me this weekend!

The note above is quite self descriptive. It has sender and receiver information, it also has a heading and a message body.

But still, this XML document does not DO anything. It is just pure information wrapped in tags. Someone must write a piece of software to send, receive or display it.
XML is Just Plain Text

XML is nothing special. It is just plain text. Software that can handle plain text can also handle XML.

However, XML-aware applications can handle the XML tags specially. The functional meaning of the tags depends on the nature of the application.
With XML You Invent Your Own Tags

The tags in the example above (like and ) are not defined in any XML standard. These tags are “invented” by the author of the XML document.

That is because the XML language has no predefined tags.

The tags used in HTML (and the structure of HTML) are predefined. HTML documents can only use tags defined in the HTML standard (like

,

, etc.).

XML allows the author to define his own tags and his own document structure.
XML is Not a Replacement for HTML

XML is a complement to HTML.

It is important to understand that XML is not a replacement for HTML. In most web applications, XML is used to transport data, while HTML is used to format and display the data.

My best description of XML is this:

XML is a software and hardware independent tool for carrying information.
XML is a W3C Recommendation

The Extensible Markup Language (XML) became a W3C Recommendation 10. February 1998.
XML is Everywhere

We have been participating in XML development since its creation. It has been amazing to see how quickly the XML standard has developed and how quickly a large number of software vendors have adopted the standard.

XML is now as important for the Web as HTML was to the foundation of the Web.

XML is everywhere. It is the most common tool for data transmissions between all sorts of applications, and becomes more and more popular in the area of storing and describing information.
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XML is used in many aspects of web development, often to simplify data storage and sharing.
XML Separates Data from HTML

If you need to display dynamic data in your HTML document, it will take a lot of work to edit the HTML each time the data changes.

With XML, data can be stored in separate XML files. This way you can concentrate on using HTML for layout and display, and be sure that changes in the underlying data will not require any changes to the HTML.

With a few lines of JavaScript, you can read an external XML file and update the data content of your HTML.

You will learn more about this in a later chapter of this tutorial.
XML Simplifies Data Sharing

In the real world, computer systems and databases contain data in incompatible formats.

XML data is stored in plain text format. This provides a software- and hardware-independent way of storing data.

This makes it much easier to create data that different applications can share.
XML Simplifies Data Transport

With XML, data can easily be exchanged between incompatible systems.

One of the most time-consuming challenges for developers is to exchange data between incompatible systems over the Internet.

Exchanging data as XML greatly reduces this complexity, since the data can be read by different incompatible applications.
XML Simplifies Platform Changes

Upgrading to new systems (hardware or software platforms), is always very time consuming. Large amounts of data must be converted and incompatible data is often lost.

XML data is stored in text format. This makes it easier to expand or upgrade to new operating systems, new applications, or new browsers, without losing data.
XML Makes Your Data More Available

Since XML is independent of hardware, software and application, XML can make your data more available and useful.

Different applications can access your data, not only in HTML pages, but also from XML data sources.

With XML, your data can be available to all kinds of “reading machines” (Handheld computers, voice machines, news feeds, etc), and make it more available for blind people, or people with other disabilities.
XML is Used to Create New Internet Languages

A lot of new Internet languages are created with XML.

Here are some examples:

* XHTML the latest version of HTML
* WSDL for describing available web services
* WAP and WML as markup languages for handheld devices
* RSS languages for news feeds
* RDF and OWL for describing resources and ontology
* SMIL for describing multimedia for the web

If Developers Have Sense

If they DO have sense, future applications will exchange their data in XML.

The future might give us word processors, spreadsheet applications and databases that can read each other’s data in a pure text format, without any conversion utilities in between.

We can only pray that all the software vendors will agree.

XML documents form a tree structure that starts at “the root” and branches to “the leaves”.
An Example XML Document

XML documents use a self-describing and simple syntax:

Tove
Jani
Reminder
Don’t forget me this weekend!

The first line is the XML declaration. It defines the XML version (1.0) and the encoding used (ISO-8859-1 = Latin-1/West European character set).

The next line describes the root element of the document (like saying: “this document is a note”):

The next 4 lines describe 4 child elements of the root (to, from, heading, and body):

Tove
Jani
Reminder
Don’t forget me this weekend!

And finally the last line defines the end of the root element:

You can assume, from this example, that the XML document contains a note to Tove from Jani.

Don’t you agree that XML is pretty self-descriptive?
XML Documents Form a Tree Structure

XML documents must contain a root element. This element is “the parent” of all other elements.
The elements in an XML document form a document tree. The tree starts at the root and branches to the lowest level of the tree.

All elements can have sub elements (child elements):

…..

The terms parent, child, and sibling are used to describe the relationships between elements. Parent elements have children. Children on the same level are called siblings (brothers or sisters).

All elements can have text content and attributes (just like in HTML).
Example:
DOM node tree

The image above represents one book in the XML below:

Everyday Italian
Giada De Laurentiis
2005
30.00

Harry Potter
J K. Rowling
2005
29.99

Learning XML
Erik T. Ray
2003
39.95

The root element in the example is . All elements in the document are contained within .

The element has 4 children: ,, , .

The syntax rules of XML are very simple and logical. The rules are easy to learn, and easy to use.
All XML Elements Must Have a Closing Tag

In HTML, you will often see elements that don’t have a closing tag:

This is a paragraph

This is another paragraph

In XML, it is illegal to omit the closing tag. All elements must have a closing tag:

This is a paragraph

This is another paragraph

Note: You might have noticed from the previous example that the XML declaration did not have a closing tag. This is not an error. The declaration is not a part of the XML document itself, and it has no closing tag.
XML Tags are Case Sensitive

XML elements are defined using XML tags.

XML tags are case sensitive. With XML, the tag is different from the tag .

Opening and closing tags must be written with the same case:

This is incorrect

This is correct

Note: “Opening and closing tags” are often referred to as “Start and end tags”. Use whatever you prefer. It is exactly the same thing.
XML Elements Must be Properly Nested

In HTML, you will often see improperly nested elements:

This text is bold and italic

In XML, all elements must be properly nested within each other:

This text is bold and italic

In the example above, “Properly nested” simply means that since the element is opened inside the element, it must be closed inside the element.
XML Documents Must Have a Root Element

XML documents must contain one element that is the parent of all other elements. This element is called the root element.

…..

XML Attribute Values Must be Quoted

XML elements can have attributes in name/value pairs just like in HTML.

In XML the attribute value must always be quoted. Study the two XML documents below. The first one is incorrect, the second is correct:

Tove
Jani

Tove
Jani

The error in the first document is that the date attribute in the note element is not quoted.
Entity References

Some characters have a special meaning in XML.

If you place a character like “<” inside an XML element, it will generate an error because the parser interprets it as the start of a new element.

This will generate an XML error:

if salary < 1000 then

To avoid this error, replace the “<” character with an entity reference:

if salary < 1000 then

There are 5 predefined entity references in XML:
< greater than
& & ampersand
' ‘ apostrophe
" ” quotation mark

Note: Only the characters “<” and “&” are strictly illegal in XML. The greater than character is legal, but it is a good habit to replace it.
Comments in XML

The syntax for writing comments in XML is similar to that of HTML.

With XML, White Space is Preserved

HTML reduces multiple white space characters to a single white space:
HTML: Hello my name is Tove
Output: Hello my name is Tove.

With XML, the white space in your document is not truncated.
XML Stores New Line as LF

In Windows applications, a new line is normally stored as a pair of characters: carriage return (CR) and line feed (LF). The character pair bears some resemblance to the typewriter actions of setting a new line. In Unix applications, a new line is normally stored as a LF character. Macintosh applications use only a CR character to store a new line.

An XML document contains XML Elements.
What is an XML Element?

An XML element is everything from (including) the element’s start tag to (including) the element’s end tag.

An element can contain other elements, simple text or a mixture of both. Elements can also have attributes.

Harry Potter
J K. Rowling
2005
29.99

Learning XML
Erik T. Ray
2003
39.95

In the example above, and have element contents, because they contain other elements. has text content because it contains text.

In the example above only has an attribute (category=”CHILDREN”).
XML Naming Rules

XML elements must follow these naming rules:

* Names can contain letters, numbers, and other characters
* Names must not start with a number or punctuation character
* Names must not start with the letters xml (or XML, or Xml, etc)
* Names cannot contain spaces

Any name can be used, no words are reserved.
Best Naming Practices

Make names descriptive. Names with an underscore separator are nice: , .

Names should be short and simple, like this: not like this: .

Avoid “-” characters. If you name something “first-name,” some software may think you want to subtract name from first.

Avoid “.” characters. If you name something “first.name,” some software may think that “name” is a property of the object “first.”

Avoid “:” characters. Colons are reserved to be used for something called namespaces (more later).

XML documents often have a corresponding database. A good practice is to use the naming rules of your database for the elements in the XML documents.

Non-English letters like éòá are perfectly legal in XML, but watch out for problems if your software vendor doesn’t support them.
XML Elements are Extensible

XML elements can be extended to carry more information.

Look at the following XML example:

Tove
Jani
Don’t forget me this weekend!

Let’s imagine that we created an application that extracted the , , and elements from the XML document to produce this output:
MESSAGE

To: Tove
From: Jani

Don’t forget me this weekend!

Imagine that the author of the XML document added some extra information to it:

2008-01-10
Tove
Jani
Reminder
Don’t forget me this weekend!

Should the application break or crash?

No. The application should still be able to find the , , and elements in the XML document and produce the same output.

One of the beauties of XML, is that it can often be extended without breaking applications.

XML elements can have attributes in the start tag, just like HTML.

Attributes provide additional information about elements.
XML Attributes

From HTML you will remember this: . The “src” attribute provides additional information about the element.

In HTML (and in XML) attributes provide additional information about elements:

Attributes often provide information that is not a part of the data. In the example below, the file type is irrelevant to the data, but important to the software that wants to manipulate the element:

computer.gif

XML Attributes Must be Quoted

Attribute values must always be enclosed in quotes, but either single or double quotes can be used. For a person’s sex, the person tag can be written like this:

or like this:

If the attribute value itself contains double quotes you can use single quotes, like in this example:

or you can use character entities:

XML Elements vs. Attributes

Take a look at these examples:

Anna
Smith

female
Anna
Smith

In the first example sex is an attribute. In the last, sex is an element. Both examples provide the same information.

There are no rules about when to use attributes and when to use elements. Attributes are handy in HTML. In XML my advice is to avoid them. Use elements instead.
My Favorite Way

The following three XML documents contain exactly the same information:

A date attribute is used in the first example:

Tove
Jani
Reminder
Don’t forget me this weekend!

A date element is used in the second example:

10/01/2008
Tove
Jani
Reminder
Don’t forget me this weekend!

An expanded date element is used in the third: (THIS IS MY FAVORITE):

10
01
2008

Tove
Jani
Reminder
Don’t forget me this weekend!

Avoid XML Attributes?

Some of the problems with using attributes are:

* attributes cannot contain multiple values (elements can)
* attributes cannot contain tree structures (elements can)
* attributes are not easily expandable (for future changes)

Attributes are difficult to read and maintain. Use elements for data. Use attributes for information that is not relevant to the data.

Don’t end up like this:

XML Attributes for Metadata

Sometimes ID references are assigned to elements. These IDs can be used to identify XML elements in much the same way as the ID attribute in HTML. This example demonstrates this:

Tove
Jani
Reminder
Don’t forget me this weekend!

Jani
Tove
Re: Reminder
I will not

The ID above is just an identifier, to identify the different notes. It is not a part of the note itself.

What I’m trying to say here is that metadata (data about data) should be stored as attributes, and that data itself should be stored as elements.

XML with correct syntax is “Well Formed” XML.

XML validated against a DTD is “Valid” XML.
Well Formed XML Documents

A “Well Formed” XML document has correct XML syntax.

The syntax rules were described in the previous chapters:

* XML documents must have a root element
* XML elements must have a closing tag
* XML tags are case sensitive
* XML elements must be properly nested
* XML attribute values must be quoted

Tove
Jani
Reminder
Don’t forget me this weekend!

Valid XML Documents

A “Valid” XML document is a “Well Formed” XML document, which also conforms to the rules of a Document Type Definition (DTD):

Tove
Jani
Reminder
Don’t forget me this weekend!

The DOCTYPE declaration in the example above, is a reference to an external DTD file. The content of the file is shown in the paragraph below.
XML DTD

The purpose of a DTD is to define the structure of an XML document. It defines the structure with a list of legal elements:

<!DOCTYPE note [

]>

If you want to study DTD, you will find our DTD tutorial on our homepage.
XML Schema

W3C supports an XML based alternative to DTD called XML Schema:

If you want to study XML Schema, you will find our Schema tutorial on our homepage.
A General XML Validator

To help you check the syntax of your XML files, we have created an XML validator to syntax-check your XML.

Please see the next chapter.
previous next

Use our XML validator to syntax-check your XML.
XML Errors Will Stop You

Errors in XML documents will stop your XML applications.

The W3C XML specification states that a program should stop processing an XML document if it finds an error. The reason is that XML software should be small, fast, and compatible.

HTML browsers will display documents with errors (like missing end tags). HTML browsers are big and incompatible because they have a lot of unnecessary code to deal with (and display) HTML errors.

With XML, errors are not allowed.
Syntax-Check Your XML

To help you syntax-check your XML, we have created an XML validator.

Paste your XML into the text area below, and syntax-check it by clicking the “Validate” button.
Tove Jani Reminder Don’t forget me this weekend!

Note: This only checks if your XML is “Well formed”. If you want to validate your XML against a DTD, see the last paragraph on this page.
Syntax-Check an XML File

You can syntax-check an XML file by typing the URL of the file into the input field below, and then click the “Validate” button:
Filename:

Note: If you get an “Access denied” error, it’s because your browser security does not allow file access across domains.

The file “note_error.xml” demonstrates your browsers error handling. If you want see an error free message, substitute the “note_error.xml” with “cd_catalog.xml”.
Validate Your XML Against a DTD

If you know DTD, you can validate your XML in the text area below.

Just add the DOCTYPE declaration to your XML and click the “Validate” button:
<!DOCTYPE note [ ]> Tove Jani Reminder Don’t forget me this weekend!

Note: Only Internet Explorer will actually check your XML against the DTD. Firefox, Mozilla, Netscape, and Opera will not.

Raw XML files can be viewed in all major browsers.

Don’t expect XML files to be displayed as HTML pages.
Viewing XML Files

-
Tove
Jani
Reminder
Don’t forget me this weekend!

Look at this XML file: note.xml

The XML document will be displayed with color-coded root and child elements. A plus (+) or minus sign (-) to the left of the elements can be clicked to expand or collapse the element structure. To view the raw XML source (without the + and – signs), select “View Page Source” or “View Source” from the browser menu.

Note: In Netscape, Opera, and Safari, only the element text will be displayed. To view the raw XML, you must right click the page and select “View Source”
Viewing an Invalid XML File

If an erroneous XML file is opened, the browser will report the error.

Look at this XML file: note_error.xml
Other XML Examples

Viewing some XML documents will help you get the XML feeling.

An XML CD catalog
This is a CD collection, stored as XML data.

An XML plant catalog
This is a plant catalog from a plant shop, stored as XML data.

A Simple Food Menu
This is a breakfast food menu from a restaurant, stored as XML data.
Why Does XML Display Like This?

XML documents do not carry information about how to display the data.

Since XML tags are “invented” by the author of the XML document, browsers do not know if a tag like

describes an HTML table or a dining table.

Without any information about how to display the data, most browsers will just display the XML document as it is.

In the next chapters, we will take a look at different solutions to the display problem, using CSS, XSLT and JavaScript.

With CSS (Cascading Style Sheets) you can add display information to an XML document.
Displaying your XML Files with CSS?

It is possible to use CSS to format an XML document.

Below is an example of how to use a CSS style sheet to format an XML document:

Take a look at this XML file: The CD catalog

Then look at this style sheet: The CSS file

Finally, view: The CD catalog formatted with the CSS file

Below is a fraction of the XML file. The second line links the XML file to the CSS file:

Empire Burlesque
Bob Dylan
USA
Columbia
10.90
1985

Hide your heart
Bonnie Tyler
UK
CBS Records
9.90
1988

.
.
.
.

Formatting XML with CSS is not the most common method.

W3C recommend using XSLT instead. See the next chapter.

With XSLT you can transform an XML document into HTML.
Displaying XML with XSLT

XSLT is the recommended style sheet language of XML.

XSLT (eXtensible Stylesheet Language Transformations) is far more sophisticated than CSS.

One way to use XSLT is to transform XML into HTML before it is displayed by the browser as demonstrated in these examples:

View the XML file, the XSLT style sheet, and View the result.

Below is a fraction of the XML file. The second line links the XML file to the XSLT file:

Belgian Waffles
$5.95

two of our famous Belgian Waffles

650

If you want to learn more about XSLT, find our XSLT tutorial on our homepage.
Transforming XML with XSLT on the Server

In the example above, the XSLT transformation is done by the browser, when the browser reads the XML file.

Different browsers may produce different result when transforming XML with XSLT. To reduce this problem the XSLT transformation can be done on the server.

View the result.

Note that the result of the output is exactly the same, either the transformation is done by the web server or by the web browser.

Most browsers have a build-in XML parser to read and manipulate XML.

The parser converts XML into a JavaScript accessible object.
Examples

W3Schools examples are browser and platform independent. These examples work in all modern browsers.

Load and parse an XML file

Load and parse an XML string
Parsing XML

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 accessed with JavaScript.

You will learn more about the XML DOM in the next chapter of this tutorial.

There are some differences between Microsoft’s XML parser and the parsers used in other browsers. The Microsoft parser supports loading of both XML files and XML strings (text), while other browsers use separate parsers. However, all parsers contain functions to traverse XML trees, access, insert, and delete nodes (elements) and their attributes.

In this tutorial we will show you how to create scripts that will work in both Internet Explorer and other browsers.

Note: When we talk about parsing XML, we often use the term “Nodes” about XML elements.
Loading XML with Microsoft’s XML Parser

Microsoft’s XML parser is built into Internet Explorer 5 and higher.

The following JavaScript fragment loads an XML document (”note.xml”) into the parser:

var xmlDoc=new ActiveXObject(”Microsoft.XMLDOM”);
xmlDoc.async=”false”;
xmlDoc.load(”note.xml”);

Example explained:

* The first line of the script above 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 “note.xml”.

The following JavaScript fragment loads a string called txt into the parser:

var xmlDoc=new ActiveXObject(”Microsoft.XMLDOM”);
xmlDoc.async=”false”;
xmlDoc.loadXML(txt);

Note: The loadXML() method is used for loading strings (text), load() is used for loading files.
XML Parser in Firefox and Other Browsers

The following JavaScript fragment loads an XML document (”note.xml”) into the parser:

var xmlDoc=document.implementation.createDocument(”",”",null);
xmlDoc.async=”false”;
xmlDoc.load(”note.xml”);

Example explained:

* The first line of the script above creates an empty 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 “note.xml”.

The following JavaScript fragment loads a string called txt into the parser:

var parser=new DOMParser();
var doc=parser.parseFromString(txt,”text/xml”);

Example explained:

* The first line of the script above creates an empty XML document object.
* The second line tells the parser to load a string called txt.

Note: Internet Explorer uses the loadXML() method to parse an XML string, while other browsers uses the DOMParser object.
Access Across Domains

For security reasons, modern browsers does not allow access across domains.

This means, that both the web page and the XML file it tries to load, must be located on the same server.

The examples on W3Schools all open XML files located on the W3Schools domain.

If you want to use the example above on one of your web pages, the XML files you load must be located on your own server. Otherwise the xmlDoc.load() method, will generate the error “Access is denied”.
The XML DOM

In the next chapter of this tutorial, you will learn how to access and retrieve data from the XML document object (the XML DOM).
The DOM (Document Object Model) defines a standard way for accessing and manipulating documents.
The XML DOM

The XML DOM (XML Document Object Model) defines a standard way for accessing and manipulating XML documents.

The DOM views XML documents as a tree-structure. All elements can be accessed through the DOM tree. Their content (text and attributes) can be modified or deleted, and new elements can be created. The elements, their text, and their attributes are all known as nodes.

In the examples below we use the following DOM reference to get the text from the element:

xmlDoc.getElementsByTagName(”to”)[0].childNodes[0].nodeValue

* xmlDoc – the XML document created by the parser.
* getElementsByTagName(”to”)[0] – the first element
* childNodes[0] – the first child of the element (the text node)
* nodeValue – the value of the node (the text itself)

You can learn more about the XML DOM in our XML DOM tutorial.
The HTML DOM

The HTML DOM (HTML Document Object Model) defines a standard way for accessing and manipulating HTML documents.

All HTML elements can be accessed through the HTML DOM.

In the examples below we use the following DOM reference to change the text of the HTML element where id=”to”:

document.getElementById(”to”).innerHTML=

* document – the HTML document
* getElementById(”to”) – the HTML element where id=”to”
* innerHTML – the inner text of the HTML element

You can learn more about the HTML DOM in our HTML DOM tutorial.
Parsing an XML File – A Cross browser Example

The following code loads an XML document (”note.xml”) into the XML parser:

function parseXML()
{
try //Internet Explorer
{
xmlDoc=new ActiveXObject(”Microsoft.XMLDOM”);
}
catch(e)
{
try //Firefox, Mozilla, Opera, etc.
{
xmlDoc=document.implementation.createDocument(”",”",null);
}
catch(e)
{
alert(e.message);
return;
}
}
xmlDoc.async=false;
xmlDoc.load(”note.xml”);

document.getElementById(”to”).innerHTML=
xmlDoc.getElementsByTagName(”to”)[0].childNodes[0].nodeValue;
document.getElementById(”from”).innerHTML=
xmlDoc.getElementsByTagName(”from”)[0].childNodes[0].nodeValue;
document.getElementById(”message”).innerHTML=
xmlDoc.getElementsByTagName(”body”)[0].childNodes[0].nodeValue;
}

W3Schools Internal Note

To:
From:
Message:

Output:
W3Schools Internal Note
To: Tove
From: Jani
Message: Don’t forget me this weekend!

Try it yourself
Important Note

To extract the text “Jani” from the XML, the syntax is:

getElementsByTagName(”from”)[0].childNodes[0].nodeValue

In the XML example there is only one tag, but you still have to specify the array index [0], because the XML parser method getElementsByTagName() returns an array of all nodes.
Parsing an XML String – A Cross browser Example

The following code loads and parses an XML string:

function parseXML()
{
text=”";
text=text+”Tove”;
text=text+”Jani”;
text=text+”Reminder”;
text=text+”Don’t forget me this weekend!”;
text=text+”";
try //Internet Explorer
{
xmlDoc=new ActiveXObject(”Microsoft.XMLDOM”);
xmlDoc.async=”false”;
xmlDoc.loadXML(text);
}
catch(e)
{
try // Firefox, Mozilla, Opera, etc.
{
parser=new DOMParser();
xmlDoc=parser.parseFromString(text,”text/xml”);
}
catch(e)
{
alert(e.message);
return;
}
}
document.getElementById(”to”).innerHTML=
xmlDoc.getElementsByTagName(”to”)[0].childNodes[0].nodeValue;
document.getElementById(”from”).innerHTML=
xmlDoc.getElementsByTagName(”from”)[0].childNodes[0].nodeValue;
document.getElementById(”message”).innerHTML=
xmlDoc.getElementsByTagName(”body”)[0].childNodes[0].nodeValue;
}

W3Schools Internal Note

To:
From:
Message:

Output:
W3Schools Internal Note
To: Tove
From: Jani
Message: Don’t forget me this weekend!

Try it yourself

Note: Internet Explorer uses the loadXML() method to parse an XML string, while other browsers uses the DOMParser object.

This chapter explains how to display XML data as HTML.
Examples

Display XML data as an HTML table
Loads data form an XML file and displays it as an HTML table.
Display XML Data in HTML

In the last chapter, we explained how to parse XML and access the DOM with JavaScript.

In this example, we loop through an XML file (cd_catalog.xml), and display each CD element as an HTML table row:

var xmlDoc=null;
if (window.ActiveXObject)
{// code for IE
xmlDoc=new ActiveXObject(”Microsoft.XMLDOM”);
}
else if (document.implementation.createDocument)
{// code for Mozilla, Firefox, Opera, etc.
xmlDoc=document.implementation.createDocument(”",”",null);
}
else
{
alert(’Your browser cannot handle this script’);
}
if (xmlDoc!=null)
{
xmlDoc.async=false;
xmlDoc.load(”cd_catalog.xml”);

document.write(”

“);

var x=xmlDoc.getElementsByTagName(”CD”);
for (i=0;i<x.length;i++)
{
document.write(”

“);
document.write(”

“);

document.write(”

“);
document.write(”

“);
}
document.write(”

“); document.write( x[i].getElementsByTagName(”ARTIST”)[0].childNodes[0].nodeValue); document.write(”

“); document.write( x[i].getElementsByTagName(”TITLE”)[0].childNodes[0].nodeValue); document.write(”

“);
}

Try it yourself: Display XML data in an HTML table
Example explained

* We check the browser, and load the XML using the correct parser
* We create an HTML table with

* We use getElementsByTagName() to get all XML CD nodes
* For each CD node, we display data from ARTIST and TITLE as table data.
* We end the table with

For more information about using JavaScript and the XML DOM, visit our XML DOM tutorial.
Access Across Domains

For security reasons, modern browsers does not allow access across domains.

This means, that both the web page and the XML file it tries to load, must be located on the same server.

The examples on W3Schools all open XML files located on the W3Schools domain.

If you want to use the example above on one of your web pages, the XML files you load must be located on your own server. Otherwise the xmlDoc.load() method, will generate the error “Access is denied”.

The XMLHttpRequest object provides a way to communicate with a server after a web page has loaded.
What is the XMLHttpRequest Object?

The XMLHttpRequest object is the developers dream, because you can:

* Update a web page with new data without reloading the page
* Request data from a server after the page has loaded
* Receive data from a server after the page has loaded
* Send data to a server in the background

The XMLHttpRequest object is supported in all modern browsers.

Example: XML HTTP communication with a server while typing input
Creating an XMLHttpRequest Object

Creating an XMLHttpRequest object is done with one single line of JavaScript.

In all modern browsers (including IE7):

var xmlhttp=new XMLHttpRequest()

In Internet Explorer 5 and 6:

var xmlhttp=new ActiveXObject(”Microsoft.XMLHTTP”)

Example

var xmlhttp;
function loadXMLDoc(url)
{
xmlhttp=null;
if (window.XMLHttpRequest)
{// code for all new browsers
xmlhttp=new XMLHttpRequest();
}
else if (window.ActiveXObject)
{// code for IE5 and IE6
xmlhttp=new ActiveXObject(”Microsoft.XMLHTTP”);
}
if (xmlhttp!=null)
{
xmlhttp.onreadystatechange=state_Change;
xmlhttp.open(”GET”,url,true);
xmlhttp.send(null);
}
else
{
alert(”Your browser does not support XMLHTTP.”);
}
}

function state_Change()
{
if (xmlhttp.readyState==4)
{// 4 = “loaded”
if (xmlhttp.status==200)
{// 200 = OK
// …our code here…
}
else
{
alert(”Problem retrieving XML data”);
}
}
}

Try it yourself using JavaScript

Note: onreadystatechange is an event handler. The value (state_Change) is the name of a function which is triggered when the state of the XMLHttpRequest object changes. States run from 0 (uninitialized) to 4 (complete). Only when the state = 4, we can execute our code.
Why Use Async=true?

Our examples use “true” in the third parameter of open().

This parameter specifies whether the request should be handled asynchronously.

True means that the script continues to run after the send() method, without waiting for a response from the server.

The onreadystatechange event complicates the code. But it is the safest way if you want to prevent the code from stopping if you don’t get a response from the server.

By setting the parameter to “false”, your can avoid the extra onreadystatechange code. Use this if it’s not important to execute the rest of the code if the request fails.

Try it yourself using JavaScript
More Examples

Load a textfile into a div element with XML HTTP

Make a HEAD request with XML HTTP

Make a specified HEAD request with XML HTTP

Display an XML file as an HTML table
Is the XMLHttpRequest Object a W3C Standard?

The XMLHttpRequest object is not specified in any W3C recommendation.

However, the W3C DOM Level 3 “Load and Save” specification contains some similar functionality, but these are not implemented in any browsers yet.

This chapter demonstrates a small XML application built with HTML and JavaScript
The XML Example Document

Look at the following XML document (”cd_catalog.xml”), that represents a CD catalog:

Empire Burlesque
Bob Dylan
USA
Columbia
10.90
1985

.
.
… more …
.

View the full “cd_catalog.xml” file in your browser.
Load the XML Document

To load the XML document (cd_catalog.xml), we use the same code as we used in the XML Parser chapter:

var xmlDoc;
if (window.ActiveXObject)
{// code for IE
xmlDoc=new ActiveXObject(”Microsoft.XMLDOM”);
}
else if (document.implementation.createDocument)
{// code for Firefox, Mozilla, Opera, etc.
xmlDoc=document.implementation.createDocument(”",”",null);
}
else
{
alert(’Your browser cannot handle this script’);
}
xmlDoc.async=false;
xmlDoc.load(”cd_catalog.xml”);

After the execution of this code, xmlDoc is an XML DOM object, accessible by JavaScript.
Display XML Data as an HTML Table

The following code displays an HTML table filled with data from the XML DOM object:

document.write(”

“);

var x=xmlDoc.getElementsByTagName(”CD”);
for (var i=0;i<x.length;i++)
{
document.write(”

“);
document.write(”

“);

document.write(”

“);
document.write(”

“);
}
document.write(”

“); document.write( x[i].getElementsByTagName(”ARTIST”)[0].childNodes[0].nodeValue); document.write(”

“); document.write( x[i].getElementsByTagName(”TITLE”)[0].childNodes[0].nodeValue); document.write(”

“);

For each CD element in the XML document, a table row is created. Each table row contains two table data cells with ARTIST and TITLE data from the current CD element.

Try it yourself: See how the XML data is displayed inside an HTML table.
Display XML Data in any HTML Element

XML data can be copied into any HTML element that can display text.

The code below is part of the section of the HTML file. It gets the XML data from the first element and displays it in the HTML element with the id=”show”:

var x=xmlDoc.getElementsByTagName(”CD”);
i=0;

function display()
{
artist=
(x[i].getElementsByTagName(”ARTIST”)[0].childNodes[0].nodeValue);
title=
(x[i].getElementsByTagName(”TITLE”)[0].childNodes[0].nodeValue);
year=
(x[i].getElementsByTagName(”YEAR”)[0].childNodes[0].nodeValue);

txt=”Artist: “+artist+”
Title: “+title+”
Year: “+year;

document.getElementById(”show”).innerHTML=txt;
}

The body of the HTML document contains an onload eventattribute that will call the display() function when the page has loaded. It also contains a

element to receive the XML data.

Try it yourself: See how the XML data is displayed inside the

element.

With the example above, you will only see data from the first CD element in the XML document. To navigate to the next line of data, you have to add some more code.
Add a Navigation Script

To add navigation to the example above, create two functions called next() and previous():

function next()
{
if (i0)
{
i–;
display();
}
}

The next() function makes sure that nothing is displayed if you already are at the last CD element, and the previous () function makes sure that nothing is displayed if you already are at the first CD element.

The next() and previous() functions are called by clicking next/previous buttons:

Try it yourself: See how you can navigate through the XML records.
All Together Now

With a little creativity you can create a full application.

If you use what you have learned on this page, and a little imagination, you can easily develop this into a full application.

Try it yourself: See how you can add a little fancy to this application.

For more information about using JavaScript and the XML DOM, visit our XML DOM tutorial.

XML Namespaces provide a method to avoid element name conflicts.
Name Conflicts

In XML, element names are defined by the developer. This often results in a conflict when trying to mix XML documents from different XML applications.

This XML carries HTML table information:

Apples

Bananas

This XML carries information about a table (a piece of furniture):

African Coffee Table
80
120

If these XML fragments were added together, there would be a name conflict. Both contain a

element, but the elements have different content and meaning.

An XML parser will not know how to handle these differences.
Solving the Name Conflict Using a Prefix

Name conflicts in XML can easily be avoided using a name prefix.

This XML carries information about an HTML table, and a piece of furniture:

Apples
Bananas

African Coffee Table
80
120

In the example above, there will be no conflict because the two

elements have different names.
XML Namespaces – The xmlns Attribute

When using prefixes in XML, a so-called namespace for the prefix must be defined.

The namespace is defined by the xmlns attribute in the start tag of an element.

The namespace declaration has the following syntax. xmlns:prefix=”URI”.

Apples
Bananas

African Coffee Table
80
120

In the example above, the xmlns attribute in the

tag give the h: and f: prefixes a qualified namespace.

When a namespace is defined for an element, all child elements with the same prefix are associated with the same namespace.

Namespaces can be declared in the elements where they are used or in the XML root element:

Apples
Bananas

African Coffee Table
80
120

Note: The namespace URI is not used by the parser to look up information.

The purpose is to give the namespace a unique name. However, often companies use the namespace as a pointer to a web page containing namespace information.

Try to go to http://www.w3.org/TR/html4/.
Uniform Resource Identifier (URI)

A Uniform Resource Identifier (URI) is a string of characters which identifies an Internet Resource.

The most common URI is the Uniform Resource Locator (URL) which identifies an Internet domain address. Another, not so common type of URI is the Universal Resource Name (URN).

In our examples we will only use URLs.
Default Namespaces

Defining a default namespace for an element saves us from using prefixes in all the child elements. It has the following syntax:

xmlns=”namespaceURI”

This XML carries HTML table information:

Apples

Bananas

This XML carries information about a piece of furniture:

African Coffee Table
80
120

Namespaces in Real Use

XSLT is an XML language that can be used to transform XML documents into other formats, like HTML.

In the XSLT document below, you can see that most of the tags are HTML tags.

The tags that are not HTML tags have the prefix xsl, identified by the namespace xmlns:xsl=”http://www.w3.org/1999/XSL/Transform”:

My CD Collection

Title	Artist

If you want to learn more about XSLT, please find our XSLT tutorial at our homepage.

TREIMA KASIH**(VASKO EDO MINTER GULTOM) AS AUTHOR XML