RDF icalendar work

Ray Ozzie has been asking some interesting questions about XML, RSS and iCalendar, and I think we have some answers, from work we have been doing for about a year on RDF and iCalendar. There has been an informal W3C taskforce on calendaring and RDF for some time, but this work got a kick-start at a workshop in Bristol, and has continued as software to convert iCalendar to RDF, testcases, chats on IRC, and email discussion. At this stage we have done about as much as we want to, and I am starting to pull together some documentation. the workshop report contains many usecases explaining why we wanted to use RDF (instead of some vanilla XML format like xCal) – most notably because we wanted to make it easy to mix together information from different namespaces with calendar information; for example foaf information about people, and geographical information, and RDF makes this easier. The result is an RDF schema and tests.
Below I’ve tried to answer some of Ray’s questions.
“Has a method to embed iCal into XML ever been approved or agreed upon? If so, let me refer to it as xCal.”
Yes – there’s something called xCal, a DTD Internet Draft, which I can’t find right now (coverpages article about it). I’m pretty sure that work has stopped on it.
“Has a method to embed xCal events/etc ever been suggested as a viable item type for RSS?”
Yes, there are at least two related activities: RSS 1.0 events module, and some attempts to embed RDFical in RSS 1.0 (try view source). The former is a draft, and one or two people are using it, but is very under-specified, making it difficult to write applications which use it. The latter is just a demo, but I think is roughly the right way to go from a modelling point of view.
“Has anyone built websites that publish venues’ event calendars in such a format for subscription/aggregation?”
Yes, LTSN economics have a site using RSS+events module; as does the SWAD-Europe project (which I work on). A related project called Skical has published Swedish events in RSS+events+ some extensions.
“Has anyone built an Outlook or Notes adapter that publishes personal or team calendars to such a feed, OR”
Sort of, see the Retsina project, which uses an older version of an RDF calendar schema and can import into outlook.
“Has anyone built an RSS aggregator that can aggregate multiple calendar RSS feeds into a desktop or web calendar UI?”
yes, I have, although it’s only a demonstrator. It’s simple to do though.
“Has anyone built an RSS aggregator that can aggregate multiple calendar RSS feeds into your Outlook or Notes personal calendar?”
Not that I have heard of….
I hope that helps. I really think that some simple way of propagating events data as RDF would be a very interesting application indeed, and I’m anxious to help it happen.

5 thoughts on “RDF icalendar work

  1. kellan

    Hey Libby,
    I don’t think “very under-specified” is quite fair. I don’t think its an appropiate format to use as the datastore for your next PIM app, or even as an over the wire scheduling format, but that doesn’t mean its under specified. Just solving a different set of problems.

  2. libby

    hi kellan, interesting post earlier. I think the rss events module is underspecified – because the specification does not say exactly what to put in each field: location, organizer and type are all free text, which makes them near-useless for apps to process. Stuff like “If the ev:startdate doesn’t specify timezone, then the timezone is implied in the ev:location.”, “Use semantic augmentation if you desire to give i.e. a URL to the place” means that an application cannot process this field effectively.
    So that’s the syntactic under-specification; as an RDF geek I also think that the semantic under-specification and confusion (events are not webpages, most notably) is confusing and makes extensions (e.g. to use a geo vocab) more difficult.
    It is a nice simple spec, and that’s why it’s attractive. Also you can use startdate and enddate ok; maybe an events module which just had this information would be good enough for some interesting things.

  3. kellan

    I hadn’t seem some of the updated, and wishy-washy language. Ugh.
    I think location, organizer, and type where all originally to be treated as free form fields, with the possible exception of organizer which some people argued should be an email address (ala iCal)
    Really geographic info should be included in via a seperate, geo vocab as you say. The idea that a field might be free form, or might be structured sucks, you’re right. In the original draft of the module the only structured data was the dates, and that is really how it should be I think.

  4. Paul

    We recently released our first product http://www.eventsherpa.com which allows users to publish and subscribe to iCalender and RDFiCal Calendars on the Windows platform. Every calendar produced and published by users is available in RDF format.
    You can see my generated homepage listing all my available calendars at http://pcowles.eventsherpa.com (contact details available in RDF here), a sample calendar at http://pcowles.eventsherpa.com/The_OReilly_Emerging_Technology_Conference/
    and the RDF version at
    Another resource for creating RDF iCalendars – free for individuals.

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