CDF (Channel Definition Format) is Microsoft's framework for creating and transmitting pushed content. Microsoft is planning to add CDF support to Internet Explorer 4.0 this summer. Netcaster is the push client contained in Netscape's new Communicator browser suite.
"[The extension] doesn't require Netscape to make any changes to the client," said Internet Explorer Product Manager Dave Fester, "And for authors and developers, it gives them the ability to write CDF that runs anywhere."
Microsoft has proposed CDF to the World Wide Web Consortium as a standard. CDF is a new collection-file format that enables a Web-site publisher to logically organize content on a site, with specific attention placed on new content. Based on the eXtensible Markup Language, CDF enables a Web site to create small files that point IE 4.0 to new content on the site.
Netscape is working on its own technology for transmitting and receiving pushed content, based on HTTP header information. Netcaster's method requires the client to check for new content by crawling through a site.
Microsoft's extension adds a new line to the CDF specification that instructs Netcaster to search only for specific CDF files, rather than surveying the whole site for updates.
A CDF file also contains information about how often a site is updated. This information can be used to set the frequency with which a browser returns to grab new information.
In addition to having new content automatically retrieved, IE 4.0 users who subscribe to a CDF-enabled site can also receive scrolling headlines within the site's channel window.