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understanding iCal - mime-directories

From: Greg FitzPatrick <greg@metamatrix.se>
Date: Thu, 31 May 2001 18:39:02 +0200
To: "Www-Rdf-Calendar@W3. Org" <www-rdf-calendar@w3.org>

I guess we are all surprised about the sudden flurry of messages on this
list.  At this point I don't want to propose anything or suggest a course of
action, though of course I have objectives just like anyone else. I would
just like to give some help to anyone wishing to understand iCal at schema

For starters there is RFC2445 - which anyone can take a look at.


RFC2445 is the basic representation of iCal and it has a structural
framework called Mime-directory. Mime-directory was actually created for
iCal and vCard, and as far as I know there are no other active uses. (note:
Chris Apple of AT&T Labs suggested a Mime-directory schema for listing
metadata in 1998) If you wish, you can think of Mime-directory as an
equivilent to XML exclusive to iCal and vCard.

Roughly the evolution of iCal (originaly called vCal... - see


for the whole story on that) ... and vCard can be though of as follows:

A formal representaion and standardization of calendars and business cards
for A2A interoperability is desired.  A language is devised -
Mime-directory, and simultaneously DTD's for calender and business card
objects are constructed using this Mime-directory format.

Mime directory is proosed in this draft: [MIMEDIR] T. Howes, M. Smith, "A
MIME Content-Type for Directory Information", INTERNET-DRAFT, November 1997.
Eventually becomming RFC 2425

XML 1.0 is formally defined in EBNF (see this article by the EBNF author:

- iCal RFC2445 is formally defined in ABNF- RFC 2234

Mime-directory has Components; sets of properties and property parameters -
there is no direct equivilent to Components in XML - Root ellements perhaps
helps as a reference. In any case Components facilitate the only "nesting"
in mime-directory

Mime-directory has Properties - the equivelent to Ellements in XML
Mime-directory has Property parameters  - the equivelent to Attributes in

example in mime-directory:

     	SUMMARY:Our Blissful Anniversary

the equivilent as XML

<?xml version="1.0" encoding="UTF-8"?>
	<DTSTART value="date">19971102</DTSTART>
	<SUMMARY>Our Blissful Anniversary</SUMMARY>
	<ATTACH FMTTYPE= "application/postscript:ftp://xyzCorp.com/pub/

- no end tags in mime-directory
- property parameters are seperated from their parent properties with ";"
and not whitespaces as in XML. There are no manditory quotes for the values
of property parameters.
- And of course all property and propery parameters are constrained by
RFC2445 (the DTD, so to speak of iCal) - But! there is one catch-all here.
Any "experimental" property or property parameter can be used in an iCal
object IF is is proceeded by "X-", so the property:
"X-DIGIPHERNELIA" is just fine.

I hope some find this helpful.

I have also loaded down Michael Arick's UML charts, but I will refrain from
commenting on them until I find my magnifying glass.

Received on Thursday, 31 May 2001 12:46:24 UTC

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