Boundary Conditions

A useful visual element that can be added to an online calendar is the Marcus Bains Line. Here is a reference and an example.

The line indicates the current time on a daily calendar.

Trying to plan a calendar for a group I belong to, I found an old thread from Jeremy with many useful links to the state of calendar solution in early 2005.

One interesting link that I found in the comments was this post from Denka, who points out the Google’s Calendar implementation is hobbled by patents. In particular, the display of an event is limited in both Google’s online calendar, or in the xml feed from that calendar, if single events are requested. (singleevents=true is a query parameter in the GData API that expands recurrent events to single events.)

For instance, I created a calendar with a single event that recurs every day, beginning on June 9th, 2007. Using the web interface to the calendar, the last day that this recurring event appears is June 7th, 2008. There are exactly 365 recurrences of the event (2008 is a leap year). You can see the calendar here, although it will be interesting to see what happens after June 9th passes.

I see the same behavior in the xml feed for the calendar. Note that that feed url has the appended query parameters singleevents=true and max-results=400. Also note that Google has used two different styles for creating parameters from compound phrases.

I manually pulled the results from that feed 6 times to figure out what the restrictions were. Here are the resulting file sizes using wget:

-rw-r--r--   1 ray  wheel   36418 Jun  5 01:06 basic?singleevents=true
-rw-r--r--   1 ray  wheel  419435 Jun  5 01:06 basic?singleevents=true&max-results=300
-rw-r--r--   1 ray  wheel  507095 Jun  5 01:06 basic?singleevents=true&max-results=364
-rw-r--r--   1 ray  wheel  508280 Jun  5 01:06 basic?singleevents=true&max-results=365
-rw-r--r--   1 ray  wheel  508280 Jun  5 01:06 basic?singleevents=true&max-results=366
-rw-r--r--   1 ray  wheel  508280 Jun  5 01:06 basic?singleevents=true&max-results=400

Once you have 365 instances of the recurring event in the feed, you don’t get any more data no matter how many you request.

Interestingly, the ics feed doesn’t have this problem and neither would the xml feed if I weren’t using the singleevents parameter. You get a single event with a start, and no end. The xml feed actually contains the VEVENT recurrence data.

Denka says that Microsoft has sewn up the patents in this area so Google had to treat recurrent events this way.

[Update: 2007-07-02] After June 9th passed, nothing changed. Both the feed and the web have only the same 365 events. There are no events after June 7, 2008. You can see this very clearly if you add the start-min parameter to the query string, as in this link which returns no results. Interestingly the date stamp on the returned file is June 5, the last day that I modified the calendar.

-rw-r--r--   1 ray  wheel  1530 Jun  5 01:41 basic?singleevents=true&start-min=2008-06-08