Keeping Track of Users

When a user is browsing through web pages using channels, then the server cannot keep track of the user. In order to collect statistics about offline browsing of a site the CHANNEL element provides two child elements namely LOG and LOGTARGET. The LOG element has only one possible value and is of the following form:

<LOG VALUE ="document:view"/>

The LOGTARGET element has an HREF attribute that identifies the URL it will be sent to, a METHOD attribute identifies the HTTP method like POST or PUT that will be used to upload the log file, and a SCOPE attribute that has one of the three values: ALL, ONLINE, or OFFLINE indicating which page views should be counted. The LOGTARGET element may have a PURGETIME child with an HOUR attribute that specifies the number of hours for which the logging information is considered valid. It may also have any number of HTTP EQUIV children used to set particular keyvalue pairs in the HTTP MIME header. The following code illustrates the use of the LOG and LOGTARGET elements.
The Base AttributeBASE is an attribute of the CHANNEL element. The value of the BASE attribute is a URL to which relative URLs in the channel can be relative. For instance, if the BASE is set to "http://www.pentasoftech.com/, then an HREF attribute can simply be 11 courses.html" instead of "http://www.pentasoftech.com/courses.html
".

The Lastmod Attribute

The value of the LAS MOD attribute is a date and time in a year monthdayThour:minutes form like 2000 10 17T1 0:15 when the page referenced by the HREF attribute was last changed. The browser detects and compares the LASTMOD date given in the CDF file with the last modified date provided by the Web server. When the content on the Web server has changed, the cache is updated with the current content. This way the browser only needs to check one file, the CDF document, for modification times rather than every file that's part of the channel. The following format describes how the LASTMOD attribute is given:

<CHANNEL LASTMOD = " 2000 10 17T1 0: 15 " >

The USAGE is a child element for both CHANNEL and ITEM elements. The USAGE element can be used in many different ways and the way is determined by the value of the VALUE attribute. The possible values for the VALUE attribute are:
1. Channel

2. Email
3.DesktopComponent

4. NONE

5. ScreenSaver

6. SoftwareUpdate

The Channel is the default value for the USAGE element. An ITEM with channel usage appears in the browser's channel bar.

If the value of the usage element is 'Email', this gives you an opportunity to send a briefer message specifying what has changed, rather than sending the entire changed page. The following code illustrate the use of Email value:

<ITEM HREF = "inform.html">

<USAGE VALUE = "Email"/>

</ITEM>

Desktop Component

Web pages or images that are directly displayed on the user's desktop are known as Desktop components. The desktop component is installed on the subscriber's desktop with a separate CDF document containing an ITEM element that points to the document to be displayed on the user's desktop. This USAGE element can contain child elements like OPENAS, HEIGHT, WIDTH, and CANRESIZE. The VALUE attribute of the OPENAS element specifies the type of file at the location in the ITEM element's HREF attribute. This should either be HTML or Image. By default the value of the OPENAS element is HTML. The VALUE attributes of the HEIGHT and WIDTH elements specify the number of pixels the item occupies on the desktop. The VALUE attribute of the CANRESIZE element can take in Yes or No which indicates whether the user can change the height and width of the component. Horizontal or vertical resizing can be independently allowed by using the CANRESIZEX and CANRESIZEY elements. The following code illustrates the use of the DesktopComponent value.

Items whose usage value is NONE are precached and are made readily available for applets and HTML pages that refer to them. These items do not appear in the channel bar. The following code illustrate the use of the NONE value.

<ITEM HREF = "penta.au" >

<USAGE= "NONE"/>

</ITEM>

slue

Items whose USAGE value is ScreenSaver point to an HTML page to replace the normal desktop after a user-specified period of inactivity. Generally, a screen saver will be written as a completely separate CDF document from the normal channel, and will require a separate download and install link. For example:

<A HREF="pentafour.cdf ">

Download and install Pentafour screen saver

</A>

Unless the subscriber has already selected the Channel Screen Saver as the system screen saver in the Display control panel, the browser will ask the user whether they want to use the Channel Screen Saver or the currently selected screen saver. Assuming they choose the Channel Screen Saver, the next time the screen is saved, the document referenced in the screen saver channel will be loaded and displayed.

The actual document displayed when the screen is saved is pointed to by the ITEM element HREF attribute. This page will generally make heavy use of DHTML, JavaScript, and other tricks to animate the screen.

Any updates to software and products can be notified using software update channels. To create a software push channel, write a CDF file with a root CHANNEL element whose USAGE element has the value SoftwareUpdate. This channel can have a title, abstract, logos, and schedule, just like any other channel. Besides the VALUE of the USAGE element, the key to a software update channel is its SOFTPKG child element. The HREF attribute of the SOFTPKG element provides a URL from which the software can be downloaded and installed. The URL should point to a compressed archive of the software in Microsoft's cabinet (CAB) format.