iCalendar validation: status report

One of the ongoing themes of my calendar aggregation project is the notion that iCalendar files are (or should be) calendar feeds in the same way that RSS and Atom files are blog and microblog feeds.

As I began to explore this idea, I realized that iCalendar feeds are all over the map in the same way that RSS feeds used to be when there wasn’t a robust, well-known validator. So began a parallel effort to improve the state of iCalendar validation.

I’ve written a series of entries on this topic, based on early observations. Now that curators for the aggregation project are finding more iCalendar feeds in the wild, we’re gathering more data for the validation effort.

Here’s the set of iCalendar-feed-generating software products that has emerged so far:

Google Calendar 70.9054
iCalcreator 2.2.8
FuseCal Software
Drupal iCal API
Intand Corporation//Tandem for Schools
Zvents Ical 
Trumba Calendar Services 0.11.5203
Meetup Inc//RemoteApi

For each city or town participating in the elmcity project, there’s a stats page that reports how two different parsers handle the set of iCalendar feeds collected for that city or town.

The first parser is the currently-available online validator based on iCal4J.

The second one parser is DDay.iCal, the component I’m using to parse and load calendars.

The outcomes reinforce what I saw in the table of results shown here. Parsers sometimes disagree about which feeds are valid, and why or why not.

My hunch is that this isn’t actually a huge problem. I think that as we:

  • collect more examples of iCalendar feeds in the wild,
  • converge on the complete set of software products that produce those feeds,
  • and run all the feeds through the available set of parsers,

we’ll find that there are maybe a dozen or so issues that account for the bulk of the discrepancies.

But that’s only a hunch. To confirm it we’ll need to gather the data and do the testing. If the elmcity project succeeds in finding and cataloging enough of the iCalendar feeds out there in the wild, we’ll have the set of feeds that need to be analyzed.

In parallel, I’ll try to run the data through more than the two parsers I’m currently using. I’m aware of iCalendar.py and vObject and will roll those in as I can. If either of these is available as service let me know, that’ll make things easier. And if there are other parsers that could be included, ping me about them. Again, if they’re available as a service, that’d be ideal.

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4 thoughts on “iCalendar validation: status report

  1. Thanks for the write up Jon, we are excited to provide ical feeds for parents, students and teachers at school districts using Tandem for Schools. We know that most of the important events that surround the family are school related. The parents at school districts with Tandem for Schools know it is really helpful to have an ical feed of all their son’s drama performances. Or their daughter’s softball games. It makes tracking the events in their digital calendars that much easier. And that’s what technology is all about, right!?

    Hope you are well! Keep up the great articles, we enjoy reading your blog.

    Bryan Otis
    President / Co – Founder

  2. > And that’s what technology is all about,
    > right!?

    What it should be about, yes.

    I’m happy to hear from you. I discovered intand.com when I was gathering calendars for the seed of my project, at http://elmcity.info/events.

    The iCalendar feed for Monadnock Regional High is available, I found, but not easily. I had to discover it, and dig out the iCalendar info using this URL template:


    And then I had to write special-case code to instantiate the template with values for the current month and year, the following month, etc.

    Would it be possible to make a more complete – and more easily accessible — iCalendar feed available from the schools your service supports?

    If so, I would love to be able to incorporate a list of those feeds into my aggregator. Schools are, as you rightly observe, a central focus of community activity. If we can establish schools as premiere publishers of iCalendar feeds, that will go a long way toward establishing the general idea of iCalendar feeds — and even more generally, feeds of all kinds — in the minds of a lot of folks who haven’t yet grasped that concept.

  3. “I think … we’ll find that there are maybe a dozen or so issues that account for the bulk of the discrepancies.”

    True. Ben Fortuna, author of iCal4j, noted in a talk at the CalConnect Roundtable XIV, held in Redmond, WA, on February 4-6, 2009, that there is a small set of recurrent issues that seem to result in a great deal of invalid iCalendar data.

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