High Quality Content by WIKIPEDIA articles! Channel Definition Format (CDF) is an XML file format used in conjunction with Microsoft Active Channel and Smart Offline Favorites technologies. Introduced in March 1997, the format is designed to "offer frequently updated collections of information, or channels, from any web server for automatic delivery to compatible receiver programs." CDF is somewhat similar to the RSS file format introduced by Netscape in 1999. CDF and Active Channel were introduced with the launch of Internet Explorer 4.0 in 1998, while Smart Offline Favorites was introduced with the launch of Internet Explorer 5.0.