XML Namespaces

XML Namespaces

It is a collection of element and attributes names associated with an XML vocabulary. XML Namespaces provide a method to avoid element name conflicts.

XML document 1

<table>

<tr>

<td>Apples</td>

<td>Bananas</td>

</tr>

</table>

XML document2

<table>

<name> Coffee Table</name> <width>80</width> <length>120</length> </table>

If these XML fragments were added together, there would be a name conflict. Both contain a <table> element, but the elements have different content and meaning. Such name conflicts in

XML can easily be avoided using a name prefix as shown below: <h:table>

<h:tr>

<h:td>Apples</h:td>

<h:td>Bananas</h:td>

</h:tr>

</h:table>

<f:table>

<f:name>African Coffee Table</f:name> <f:width>80</f:width> <f:length>120</f:length>

</f:table>

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"

For example,

<h:table xmlns:h="http://www.w3.org/table"> <h:tr>

<h:td>Apples</h:td>

<h:td>Bananas</h:td>

</h:tr>

</h:table>

<f:table xmlns:f="http://www.w3.org/furniture"> <f:name>African Coffee Table</f:name> <f:width>80</f:width> <f:length>120</f:length>

</f:table>

Default namespace

Default xml namespace uri for elements of a document is xmlns:http://www.w3.org/1999/xhtml

RSS

 RSS stands for Rich Site Summary.

 RSS is a format for delivering regularly changing web content. Many news-related sites and other online publishers syndicate their content as an RSS Feed to whoever wants it.

RSS allows you to syndicate your site content.

RSS defines an easy way to share and view headlines and content.

With RSS it is possible to distribute up-to-date web content from one web site to thousands of other web sites around the world.

RSS allows fast browsing for news and updates. RSS was designed to show selected data.

Distributing your content using RSS will involve creating one file that contains your content.

This file will reside on your server to enable other web sites to display your channel. You

can    update your channel simply by updating your file.

Without RSS, users will have to check your site daily for new updates. This may be too timeconsuming for many users. With an RSS feed, they can check your site faster using an RSS aggregator (a site or program that gathers and sorts out RSS feeds) since RSS data is small and fast-loading

RSS is useful for web sites that are updated frequently, like:

1. News sites - Lists news with title, date and descriptions

2. Companies - Lists news and new products

3. Calendars - Lists upcoming events and important days

4. Site changes - Lists changed pages or new pages

RSS files can be automatically updated

RSS allows personalized views for different sites

RSS is written in XML

With RSS it is possible to distribute up-to-date web content from one web site to thousands of other web sites around the world.

RSS allows fast browsing for news and updates. RSS was designed to show selected data.

Distributing your content using RSS will involve creating one file that contains your content.

This file will reside on your server to enable other web sites to display your channel. You can update your channel simply by updating your file.

Without RSS, users will have to check your site daily for new updates. This may be too time consuming for many users. With an RSS feed, they can check your site faster using an RSS aggregator (a site or program that gathers and sorts out RSS feeds) since RSS data is small and fast-loading

RSS is useful for web sites that are updated frequently, like:

1. News sites - Lists news with title, date and descriptions

2. Companies - Lists news and new products

3. Calendars - Lists upcoming events and important days

4. Site changes - Lists changed pages or new pages

Creating an RSS File

Your first step will be to identify your file. To do this, place the following code at the top of your text file.

<?xml version="1.0"?> <rss version="0.91">

Your next step will be to create your channel header. The "channel" tag indicates that you are beginning a new channel.

<channel>

<title>Web-Source.net Syndication</title> <link>http://www.web-source.net</link>

<description>Web Development article syndication feeds!</description> <language>en-us</language>

The "title" tag indicates the name of your channel. The "link" tag will contain a link to your website. The "description" tag describes your channel and the "language" tag indicates that you're writing in US English.

<item>

<title> Creating A Customized Marquee </title> <link>http://www.example.com/tips.htm</link> <description>

Learn how to create a customized marquee for your web </description>

</item>

Your final step will be to close your channel by adding the following tags:

</channel>

</rss>

Save your new file with .rss file extension and upload it to your server. And now, you're ready to share your content.

JavaScript and XML: AJAX

AJAX:

-  AJAX stands for Asynchronous JavaScript and XML

-  AJAX allows web pages to be updated asynchronously by exchanging small amounts of data with the server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.

- Using Ajax,

o Update a web page with new data without reloading the page o Request data from a server after the page has loaded

o Receive data from a server after the page has loaded o Send data to a server in the background

-  AJAX allows updating parts of a web page, without reloading the whole page.

-   With Ajax, web applications can also retrieve data from the server asynchronously in the background without interfering with the display and behavior of the existing page.

-  Ajax is combination of

o HTML o XML o CSS

o JavaScript

o JavaScript DOM

o XMLHttpRequest in asynchronous mode.

1.     Asynchronous: This means that when you send a request, you wait for the response to come back, but are free to do other things while you wait. The response probably won’t come back immediately, so you set up a function that will wait for the response to be sent back by the server, and react to it once that happens.

2.     JavaScript JavaScript is used to make a request to the server. Once the response is returned by the server, you will generally use some more JavaScript to modify the current page’s document object model in some way to show the user that the submission went through successfully.

3.        XML The data that you receive back from the server will often be packaged up as a snippet of XML, so that it can be easily processed with JavaScript. This data can be anything you want, and as long as you want.

How AJAX works?

XMLHttpRequest - Constructor for other host objects allow a JavaScript program to send

an

HTTP request to a server and receive back a response containing an XML document. The following program illustrates the use of XMLHttpRequest.

Example <html> <head>

<script type="text/javascript"> function dataData()

{

var xmlhttp=new XMLHttpRequest(); // create XMLHttpRequest to exchange data with server

var obj= getElementById("myDiv"); xmlhttp.onreadystatechange=function()

{

if (xmlhttp.readyState==4 && xmlhttp.status==200)

{

obj=xmlhttp.responseText;

}

}

xmlhttp.open("GET",”data.txt”, true); xmlhttp.send();

}

</script>

</head>

<body><form>

<div id="myDiv">Let AJAX change this text</div>

<input type="button" value=”Change Content” onclick=”getData()”; /> </form></body>

</html>