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Channel Definition Format

The Channel Definition Format was a Microsoft file format for syndication based on XML. It was designed for its Active Channels technology and got extended for Active Desktop integration or for OSD.

Specification (or lack thereof)

CDF does not have a standardized specification: a note was sent to the W3C in 1997 with a very early draft of the format, with the intention of later making it into a standard, but there were no further updates. The Microsoft docs of that time are the same as this draft.

The latest documentation, from 2002, describes a format that varies a lot from that W3C note.

There is no official DTD or XSD. Someone wrote a DTD with support for the Active Desktop and OSD extensions.

I wrote my own XSD files to help me use this format in ITSB:

The CDF 0.4 XSD includes the CDF Extensions for Active Desktop Items.

Support

CDF was supported by Internet Explorer 4 to 7, and no other software is known to have supported this format.

The format was created and implemented in IE4 while XML was still a draft, causing some valid XML documents to not be understood properly by IE4, and all the sample CDF files provided with IE4 to make XML parsers scream.

Support was dropped in 2009 with the release of IE8 as it lost against RSS, and as Microsoft's dedicated RSS team implemented RSS support in IE7.

Notable features

  • Scheduling options to avoid useless synchronizations
  • Nested channels (merge multiple feeds into one)
  • Custom icons in the IE favorites sidebar
  • Customization of IE's crawling behavior when making a website available offline, using <LINK REL="OFFLINE" HREF="...cdf">
  • Active Desktop integration to display articles on the desktop
  • Integration with Open Software Description to send software updates

Usage

I use this format in ITSB to provide separate channels generated from each RSS feed, or channels that group channels together. This second form usually causes Internet Explorer to lag heavily due to the few megabytes of items it is downloading in a single file. All of those CDF files have been tested and confirmed to be working with Internet Explorer 6 SP1 on Windows 2000 SP4.

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