Vetting iCalendar files

In my blog post of December 27, 2010, In calendaring, success means the right thing, the right way!, I talked about downloading iCalendar .ics files from university sports web sites, and importing these events into different calendaring systems to ascertain whether the event data was interpreted the same way in each system. I discovered that more often than not, the events were not represented as intended as they did not conform to, or fully exploit the capabilities of, the iCalendar specification. I concluded that post with “It is well worth your while to run through the exercise of exporting your public events, and importing them into the more widely used calendaring systems to ensure that you have, indeed, done the right thing the right way.”

Among the tools I used for this exercise was the iCalendar Validator developed by Doug Day and Jon Udell. On our CalConnect website, we provide a link to a web instance that you can validate iCalendar files against (See As noted, on the web site,, “technically speaking, the word “validation” is somewhat incorrect, as there are no definitive rules we can follow to guarantee a calendar is valid (or invalid). Perhaps a better description would be “proofing” tools; however, for practical reasons I call it “validation”. Or put another way, among other things, there is no way to insure the syntax of the iCalendar file implements the intended semantics.

Shortly thereafter, I contacted Doug Day to share with him some “helpful” suggestions I had for making iCalendar Validator even better, such as displaying how many events are without any timezone reference. We also discussed the possibility of Doug open sourcing the code, as the iCalendar Validator is just one of many projects competing for his time.

Last month, Doug did just that, or in his own words,

“icalvalid, the iCalendar Validator found at, is now open-source! It’s hosted on github at This validation utility was created to validate calendaring data against the iCalendar standard (RFC 5545). We’re looking for contributors – please consider contributing your time/efforts to help improve the validator!”

I commend Doug for sharing his work in this open fashion. And, for those of you who become contributors, I would still love to see a display of how many events are represented without a timezone reference.

Gary Schwartz
President, The Calendaring and Scheduling Consortium

CalConnect Statement on the Olson Timezone Database and related suit

CalConnect has always been interested in timezone data because accurate and timely timezone information is essential to calendaring and scheduling. We have done considerable work in the area and have always been impressed by the Olson volunteer team and Olson Database.

The Timezone database, edited and managed by Arthur David Olson, provides a comprehensive source for timezone data including daylight savings rules, which often change at short notice in many regions of the world. Many editions of the Timezone database are produced each year to address these changes as quickly as possible.

The Timezone database has been the trusted source for timezone information for a very long time and is a critical component of nearly all major computer systems and Internet operations. This includes desktop computers, servers, databases, mobile devices, telecommunications equipment, logistics, embedded control systems, and many others. Online, web-based applications such as payment systems, package tracking, airline reservations systems also depend heavily of timezone data.

Many of these issues were exposed not just for calendaring systems but systems on all forms of devices in 2005-2007 as a result of the passage of the Extended Daylight Savings Time legislation by Congress. The potential impact even then was widespread although the impact was primarily on countries in North and Central America and to some degree South America. This was only a single change to a few timezones, admittedly that affected a good portion of the world. In one sense this was the reverse of the problem we are facing now, but the probable impact today is much larger, especially as enormous numbers have mobile devices which offer services that depend on currency of timezone data.

Disruption to the publication and availability of the Timezone database will cause significant harm to individuals and organizations using computer systems, either directly or indirectly. This harm will get worse over time as changes to timezones and daylight savings time rules fail to be tracked by the database. Computer systems will continue to use the last available database, or perhaps even splinter into groups who manage their own updates separately. The later situation will cause even more confusion as different systems may have different times even though they are in the same location.

It is the opinion of CalConnect that the Timezone database MUST be re-instated, made publicly available, and continue to be maintained in an open, inclusive and consensual fashion. This needs to be done as soon as possible so that the discussions on pending changes can continue, and appropriate database updates produced in a timely fashion.

Basic information about the Olson Timezone Database and the lawsuit may be found on Wikipedia.

Dave Thewlis
Executive Director, CalConnect – The Calendaring and Scheduling Consortium

Friday afternoon: wrapping up CalConnect XXII in Prague

The meeting is drawing to a close with the last Technical Committee session, followed by the wrapup and our Plenary meeting. It’s been a great five days, although quite tiring as always. We are very happy with the European involvement, including the presence of representatives from four non-members, which has injected new perspectives and concerns into the technical discussions to the benefit of everyone.

Additionally the “CalConnect Internationally” discussion, about what CalConnect should do to better support and allow more involvement from people based in Europe, produced a number of ideas in a variety of areas, and we have suggestions for our Technical Committee operating processes, our Steering Committee and our Board on possibilities going forward.

We are also delighted to announce that Apple will host CalConnect XXIII, which will be held the week of January 30 – February 3 in Cupertino, California.

CalConnect Roundtable as of Thursday afternoon 6 October

The Roundtable technical conference is going well. We have 20 participants which for our very first full CalConnect event in Europe is pretty respectable, and this includes four non-member organizations (ARC Informatique, DHL, Intel open source lab, and Stylite AG.

We moved the regular Technical Committee sessions to the afternoon to allow people in North America to join the sessions via GotoMeeting, which gave us time for symposia and workshops Thursday and Friday morning. This morning the symposia were “The Evolution of Internet Calendaring Standards” and “Integrating Internet Calendaring Systems into products and services”.

Friday morning we is a workshop on Tasks (VTODOs) and how iCalendar should be extended to support new requirements such as project management, energy scheduling, and so forth. And we will have a BOF on “CalConnect Internationally”, to discuss how CalConnect can make itself more accessible and available to international members (in particular Europe, at the moment). I’ve heard some good ideas so far and look forward to the group discussion, as it will certainly inform CalConnect’s decisions about going forward internationally.

Dave Thewlis
CalConnect Executive Director

Interoperability Testing Underway at CalConnect XXII

Today is the second day of the interoperability testing event at CalConnect XXII in Prague, hosted by Kerio Technologies. Fifteen people present from eight organizations and individual members, plus one testing remotely.

  • Andrew McMillan – DAViCal server and aCal Android client
  • Apple – Apple clients and servers
  • Intel – SyncEvolution open source client
  • Kerio Technologies – Kerio Connect
  • Oracle – Oracle Communications Calendar Server
  • RPI – Bedework open source CalDAV server
  • Stylite AG – EGroupware
  • Synchronica – Synchronica Mobile Gateway

The test event will continue until noon Wednesday; the Roundtable Technical Conference begins at 13:00 on Wednesday.


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