[ietf-calsify] XML iCalendar issues and questions

Steven Lees Steven.Lees at microsoft.com
Tue Jul 21 16:44:42 PDT 2009


I haven't seen much public comment on the XML iCalendar draft (http://www.ietf.org/id/draft-daboo-et-al-icalendar-in-xml-00.txt) that Cyrus, Mike, and I submitted in June. I thought it might be helpful to write up a quick summary of some of the issues that people have mentioned to me. Since one of our goals is to have consistency between vCard-in-XML and iCalendar-in-XML, I've also written up my understanding of how the vCard-XML draft handles these issues.

1) Date-time format:
The xCalendar draft breaks out date/time values into separate XML elements for year/month/day and hour/minute/second. The main reason for choosing this format was to make it easier for implementers who want to transform the XML into a presentation format like HTML. The separate elements mean that no additional parsing is necessary. It does significantly increase the size of the XML format, however. One compromise that has been suggested is to make the XML element names smaller, i.e. <y> instead of <year>.

Here's an example:
          <date-time utc="yes">

The xCard draft embeds the vCard time value in a single XML element:, which is obviously much more compact:


2) Extensibility:
The xCalendar draft describes two kinds of extensions. Extensions that originate in iCal with the "x-" prefix are converted to XML elements with the same name (but in lowercase). Those extensions are in the same XML namespace as other xCalendar elements. This makes it straightforward to convert those extensions back to the iCal format. Other XML extension elements are allowed as well, but such extensions must not be in the xCalendar XML namespace. Such extensions are not convertible to the iCal format.

In contrast, the xCard draft describes only the second kind of extension: those that are in a separate XML namespace. As far as I can tell, the xCard draft doesn't describe a way to convert those extensions to the vCard format.

3) XML attributes:
The xCalendar draft currently uses attributes in two places. There is a "utc" attribute on date-time elements, and a "sign" attribute on duration elements.

The xCard draft doesn't appear to use any XML attributes. This allows a simple transformation to key/value formats like JSON.

It would be great to hear opinions on these or other issues. If you're attending IETF next week in Stockholm, the topic of XML formats for vCard and iCalendar is on the agenda for the vcarddav working group on Tuesday July 28: http://www.ietf.org/mail-archive/web/vcarddav/current/msg01105.html.


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