An open standard created by Microsoft for Microsoft Internet Explorer version 4 (and proposed as a standard to the World Wide Web Consortium) that defines a «smart pull» technology for webcasting information to users desktops. Based on the Extensible Markup Language (XML), Channel Definition Format (CDF) lets administrators create Active Channels for delivery of content through the users Web browser, and Active Desktop elements and channel screen savers for delivery directly to the users desktops.
Channel content can be personalized, and delivery can be scheduled according to users needs and preferences. Using CDF also reduces server load and allows delivery of just the needed content, instead of requiring users to download large quantities of unnecessary content.
Let’s consider the delivery of Web content to the user’s browser using Active Channels. A Web site can be made into an Active Channel through the addition of a CDF file. The CDF file is a simple text file that is formatted using XML. It forms a kind of table of contents of the logical subset of the Web site that comprises the Active Channel. A link is then created to the CDF file on the Web site. The user clicks the link to subscribe to the Active Channel and download the CDF file. The Active Channel then appears on the channel bar on the user’s desktop. The content for the channel is downloaded to a cache on the user’s system. Channel updates are accomplished by scheduled Web crawls, using either the publisher’s predefined schedule or a user’s customized one. Users can also receive updates to channels by e-mail.
Some of the advantages of using CDF for the distribution of Web information to users include
CDF is not true webcasting in the sense of Internet Protocol (IP) multicasting because it is a “pull” technology. True webcasting is supported by Microsoft NetShow for delivery of content using IP multicasting.