hcalendar-brainstorming

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hCalendar Brainstorming

to-do: this page could use just a bit more clean-up and reorganization. - Tantek

This page is for trying out and documenting ways of using hCalendar which may involve more details than currently in the specification.

If you have a question, please check the hCalendar FAQ, and ask new questions on the mailing lists first.

Authors

hCalendar authoring best practices

Tabular event calendars

Many calendars are posted in tabular form, where the headings on the columns and rows have property values that apply to the cells which themselves are events. E.g. many conferences have multiple tracks and post names of rooms (LOCATION) as column headers, and time slots (DTSTART, DTEND) as row headers.

Here is a description of how to parse such markup into an iCalendar stream. This has been implemented in X2V and deployed.

TO DO: document a "How To" for publishers looking to mark up tabular event listings.

To enable mark these up with hCalendar, we must parse additional semantic attributes from HTML4.

When parsing, in addition to the special case rules documented in hcard-parsing:

  • If the element is a table data cell <td>, then:
    1. parse its "headers" attribute as a space separated set of local IDs
    2. find the <td> and <th> elements referenced by those IDs (call them header cells) and consider them part of the element being parsed as follows:
      1. Treat the header cells as children of the element, ordered by the order of ids in its "headers" attribute, immediately following the last child node (text or element) or the element. (The basic idea is that the content from those header cells is used to construct the VEVENT, but secondary to (AFTER) the content in the data cell itself, so that the data cell can customize/override part of the data in the header, e.g. if the header cell included both start time and location, and the event was being held at a different location).
      2. Parse the "axis" attribute of a header cell as a comma-separated list of categories. These categories must be used in addition to (and before) any class names on that header cell for determining whether it is a property of the VEVENT.

Real world example in the wild of a tabular event calendar marked up in this fashion: Web Essentials 05 Session program.

Note: We have gained sufficient experience with this that we should formalize this in both hcard-parsing and hcalendar-parsing since the table cell headers and axis attributes technique is generic to all class name microformats. The specific use case of how to author a tabular display of events should be documented in hcalendar-authoring. Tantek


hCard locations

In iCalendar (and thus hCalendar), the LOCATION property is just a text string. In practice however, much event content contains some amount of structure for the location, often a specific venue with name, address etc. Venues are often organizations and are thus conducive to being marked up as hCards.

Taking the example from the hCalendar spec: 

<span class="vevent">
 <a class="url" href="http://www.web2con.com/">
  <span class="summary">Web 2.0 Conference</span>: 
  <abbr class="dtstart" title="2005-10-05">October 5</abbr>-
  <abbr class="dtend" title="2005-10-08">7</abbr>,
 at the <span class="location">Argent Hotel, San Francisco, CA</span>
 </a>
</span>

Clearly the "Argent Hotel" is a venue, and thus could be marked up as an hCard itself: 

 <span class="location vcard">
  <span class="fn org">Argent Hotel</span>, 
  <span class="adr"><span class="locality">San Francisco</span>, <span class="region">CA</span></span>
 </span>

Thus in the context of the entire vevent this example would become: 

<span class="vevent">
 <a class="url" href="http://www.web2con.com/">
  <span class="summary">Web 2.0 Conference</span>: 
  <abbr class="dtstart" title="2005-10-05">October 5</abbr>-
  <abbr class="dtend" title="2005-10-08">7</abbr>,
 at the <span class="location vcard">
   <span class="fn org">Argent Hotel</span>, 
   <span class="adr"><span class="locality">San Francisco</span>, <span class="region">CA</span></span>
  </span>
 </a>
</span>

The advantage of marking up the location with explicit hCard semantics is that it enables much better identification and pivoting of locations of events.

For a real world example of this in practice see Jeremy Keith's excellent SXSW 2006 event page: http://austin.adactio.com/ where all the events contain locations marked up as hCards with geo properties as well which then aid in locating the precise locations on a map.

Note: We have gained sufficient experience with this that we should formalize this in hcalendar-authoring. Tantek


iCalendar generation best practices

Along with the four base properties, you can define addtional properties through the use of the x-prop property. For best-practices for hCal to iCal transformers, it would be helpful if the transforming application added the following x-* properties:

X-FROM-URL

  • X-FROM-URL. The value of this property would be the URL of the page where the iCal representation was generated.
X-FROM-URL:http://example.com/page-containing-hCal-encoding.html

Note: We have gained sufficient experience with this that we should formalize this in hcalendar-parsing. Tantek

X-WR-CALNAME

  • X-WR-CALNAME. iCal.app recognizes this property as the "calendar name" for subscribed calendars. Thus transforming applications *should* take the <title>...</title> from the page being parsed, optionally append " events", and use that value for the X-WR-CALNAME property in the resulting feed. E.g. if the page had <title>Example Home Page</title> then the .ics output should have as part of the vcalendar object:
X-WR-CALNAME:Example Home Page

Note: We have gained sufficient experience with this that we should formalize this in hcalendar-parsing. Tantek

iCalendar examples in hCalendar

This is a growing example case written in iCal format and transformed to the corresponding XHTML. These conversions are open to community input. See hcalendar-examples for current work. 

BEGIN:VEVENT
CATEGORIES:foo,bar
SUMMARY: Short Title
DESCRIPTION: Full Description
DTSTART;VALUE=DATE:20040101
DTEND:20040101T235959Z
RRULE:FREQ=YEARLY;UNTIL=20080102T000000Z
URL;WORK:http://example.com
ATTENDEE;ROLE=CHAIR:MAILTO:JohnDoe@example.com
GEO:37.386013;-122.082932
END:VEVENT

<p class="vevent">
<!-- @@ how to deal with Whitespace issues in lists 'foo, bar' -->
Categories:
<ul class="categories">
<li>foo</li>
<li>bar</li>
</ul>
<a href="http://example.com" class="summary">Short Title</a>
<span class="description">description</span>
<span class="geo"><span class="Lat">37.386013</span> <span class="Lon">-122.082932</span></span>

<!-- This currently does not take into consideration the VALUE=DATE -->
<!-- The transforming application could attempt to detect the proper format and add params as needed? -->
Date: <em class="dtstart">20040101</em> - <em class="dtend">20040101T235959Z</em>

<!-- any thoughts to better encode attendee -->
<!-- the ROLE must be of a known type, but one of type is x-name (user-specified) -->
<!-- therefore there is no solid way to know "chair" refers to a ROLE parameter -->
<a class="attendee chair" href="mailto:JohnDoe@example.com">John Doe</a>

<!-- this messy, but works. Is there a better way? -->
<p class="rrule">The event will be held <span class="freq">yearly</span> until <span class=""until">20080102T000000Z</span>.</p>

</p>

@@-need to look at nested tag examples 

XHTML
<span class="description"><span class="summary">Short Title</span> to a longer article</span>

vCal
SUMMARY:Short Title
DESCRIPTION:Short Title to a longer article


Examples from RFC 2445

With the abbr's title attribute being used rather than the node value, the actual data could vary and still represent the same vcalendar. 

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//hacksw/handcal//NONSGML v1.0//EN
BEGIN:VEVENT
DTSTART:19970714T170000Z
DTEND:19970715T035959Z
SUMMARY:Bastille Day Party
END:VEVENT
END:VCALENDAR

<span class="vcalendar">
  <span class="vevent">
    <abbr class="dtstart" title="19970714T170000Z">July 14th</abbr>
    <abbr class="dtend" title="19970715T035959Z"></abbr>
    <span class="summary">Bastille Day Party</span>
  </span>
</span>

UID handling

The UID in iCal is represented in HTML as the id attribute in these examples. Any valid id in HTML is a valid UID in iCal, but not the contrapositive, a valid UID is NOT a valid HTML id. HTML ids can only start with a letter, not a number. 

BEGIN:VEVENT
UID:19970901T130000Z-123401@host.com
DTSTAMP:19970901T1300Z
DTSTART:19970903T163000Z
DTEND:19970903T190000Z
SUMMARY:Annual Employee Review
CLASS:PRIVATE
CATEGORIES:BUSINESS,HUMAN RESOURCES
END:VEVENT

<span class="vcalendar">
  <span class="vevent" id="19970901T130000Z-123402@host.com">
    <abbr class="dtstamp" title="19970901T1300Z"></abbr>
    <abbr class="dtstart" title="19970903T163000Z">September 3rd, 4:30pm</abbr>-
    <abbr class="dtend" title="19970903T190000Z">7:00pm</abbr>
    <span class="summary">Annual Employee Review</span>
    <span class="class">private</span>
    <ul class="categories">
      <li>BUSINESS</li>
      <li>HUMAN RESOURCES</li>
    </ul>
  </span>
</span>

BEGIN:VCALENDAR
BEGIN:VEVENT
UID:19970901T130000Z-123402@host.com
DTSTAMP:19970901T1300Z
DTSTART:19970401T163000Z
DTEND:19970402T010000Z
SUMMARY:Laurel is in sensitivity awareness class.
CLASS:PUBLIC
CATEGORIES:BUSINESS,HUMAN RESOURCES
TRANSP:TRANSPARENT
END:VEVENT
END:VCALENDAR

<span class="vcalendar">
  <span class="vevent" id="19970901T130000Z-123402@host.com">
    <abbr class="dtstamp" title="19970901T1300Z"></abbr>
    <abbr class="dtstart" title="19970401T163000Z">April 1st 4:30pm</abbr>-
    <abbr class="dtend" title="19970402T010000Z">1:00am</abbr>
    <span class="summary">Laurel is in sensitivity awareness class.</span>
    <span class="class">PUBLIC</span>
    <ul class="categories">
      <li>BUSINESS</li>
      <li>HUMAN RESOURCES</li>
    </ul>
    <span class="transp">Transparent</span>
  </span>
</span>

RRULE handling

The way RRULE is encoded should be discussed. 

BEGIN:VEVENT
UID:19970901T130000Z-123403@host.com
DTSTAMP:19970901T1300Z
DTSTART:19971102
SUMMARY:Our Blissful Anniversary
CLASS:CONFIDENTIAL
CATEGORIES:ANNIVERSARY,PERSONAL,SPECIAL OCCASION
RRULE:FREQ=YEARLY
END:VEVENT

<span class="vcalendar">
  <span class="vevent" id="19970901T130000Z-123403@host.com">
    <abbr class="dtstart" title="19970901T1300Z"></abbr>
    <abbr class="dtend" title="19971102">November 2nd</abbr>
    <span class="summary">Our Blissful Anniversary</span>
    <span class="class">CONFIDENTIAL</span>
    <ul class="categories">
      <li>ANNIVERSARY</li>
      <li>PERSONAL</li>
      <li>SPECIAL OCCASION</li>
    </ul>
    <span class="rrule"><span class="freq">YEARLY</span></span>
  </span>
</span>

Examples from real world event sites

W3C Meetings

I just got email announcing the dates of another W3C meeting. I don't think it's marked up with hCalendar. I could mark it up myself, like I did for the TP day/week schedule, but it might not stick. Somehow I got our syndicated news markup (precursor to hAtom) to stick, i.e. to become part of the norm in the W3C comm team. I wonder if I could pull that off for calendars.

My first thought is authoring tools, but I don't think I can wait that long. Next thought is instant-feedback checking tools... X2V is really handy, but can't be used for confidential pages (and many/most calendars I use are not public). So.. how about some in-browser javascript "yes, you got it right!" or "hmm... that looks like a date; is there an event you didn't mark up?" feedback? I think I saw something like that in hCalendar implementations.

DanC 09:00, 3 Feb 2006 (PST)

Laughing Squid

Laughing Squid had the following multiple occurence event example: 

Thu, Apr 7 : Tu/Wed: 12-4pm Th/Fr/Sat 12-7pm Sun 12-6pm

In addition, later on in the description, it says: 

April 7-21, 2005

This is actually quite a non-trivial example, because the event lasts for different durations on different days (4 hours, 7 hours, 6 hours).

Because of the differing durations, the specification requires that *each* instance of this recurring event be explicitly specified.

But first we markup the starting date and time explicitly: 

<abbr class="dtstart" title="20050407T1200-0700">Thu, Apr 7</abbr> :

Then we put in the quite lengthy explicit specification of every other time the event occurs, marked up around the human readable description. 

<abbr class="rdate" title="20050407T1200-0700/PT7H, 20050408T1200-0700/PT7H, 
20050409T1200-0700/PT7H, 20050410T1200-0700/PT6H, 20050412T1200-0700/PT4H, 
20050413T1200-0700/PT4H, 200504014T1200-0700/PT7H, 20050415T1200-0700/PT7H, 
20050416T1200-0700/PT7H, 20050417T1200-0700/PT6H, 20050419T1200-0700/PT4H, 
20050420T1200-0700/PT4H, 20050421T1200-0700/PT7H" >
Tu/Wed: 12-4pm Th/Fr/Sat 12-7pm Sun 12-6pm
</abbr>

The RDATE "PERIOD" format is fairly straightforward. You simply list *each* occurrence of the event, separated by commas. Each occurrence consists of the ISO8601 datetime of the start of the event, followed by a slash "/", followed by *either* the duration of the event (e.g. 7 hours = PT7H), *or* a complete ISO8601 datetime of the end of the event. I chose to use the duration of the event for this example for reason of brevity.

Note that "value=period:" is unnecessary in the rdate value since the parser can infer "value=period:" from the presence of a "/" in the title attribute value.

With simpler repeating events, or perhaps events which only repeat a day or two, their hCalendar markup may be more illustrative of how to do this in a general way.

CSS Styles

Since the hCal properties are added in as HTML class names, you can style them with CSS class selectors along with other HTML class names. You are free to style these properties in any fashion you want (see specific notes), but here are a few examples that you can use.

Preserving White-space

If you are encoding data that requires tabs, returns, or other white-space to be perserved you can use the following CSS property to do so in HTML. 

<span style="white-space: pre">
This white-space
will be
preserved
</span>

white-space can take one of three different parameters; normal, pre, and no-wrap.

Not recommended

The following CSS styling techniques are not recommended:

Hiding Data

It is possible to encode additional data without it being displayed in the HTML, by using the CSS style property 'display'. 

<span style="display:none">Hidden Data</span>

This data will be found by any transforming application and will be properly encoded into an iCal file.

You SHOULD NOT do this because it violates the visibility priniciple.

hCalendar for timelines

There have been some interesting discussions about how to use hCalendar for marking up timelines. Here are some pointers:

Open Questions

Undecided Encodings of Certain Property Attributes

There are several attributes that still need to be discussed about how to property encode them into HTML.

For example the RSVP and ROLE attrbutes: ATTENDEE;RSVP=TRUE;ROLE=REQ-PARTICIPANT:MAILTO:jsmith@host.com or ATTENDEE:CUTYPE=GROUP:MAILTO:john@host.com

Other attributes include:

  • Delegate-To
  • Delegate-from
  • Sent-By
  • Member
  • Partstat
  • CN
  • DIR

Then all the enumerated possible values for each of these

General Questions

Q: Should Transforming applications purely extract the information and ignore validity? or should there be some checking, or should this be left to the importing application? (i.e. DTSTART;VALUE=DATE: This-Is-Not-a-proper-date)

A: The simpler the better. Other than checking for perhaps X(HT)ML validity, it should be a simple translator, because presumably the receiving iCalendar application has to have malformed .ics handling already. Let's avoid duplicating that. -- Tantek Çelik

Q: What about multiple of the instances same vCal entity? (two instances of DTSTART) Is this left up to the importing application, or should the XSLT transformation fail?

A: Same as previous. Leave it up to the importing application to interpret it per the iCalendar spec, e.g. what does RFC2445 say about two instances of DTSTART? -- Tantek Çelik

From RFC2445: 4.1.2 Multiple Values Some properties defined in the iCalendar object can have multiple values. The general rule for encoding multi-valued items is to simply create a new content line for each value, including the property name. However, it should be noted that some properties support encoding multiple values in a single property by separating the values with a COMMA character (US-ASCII decimal 44). Individual property definitions should be consulted for determining whether a specific property allows multiple values and in which of these two forms.

Other than that, it does not mention what to do ABOUT invalid data, or which of the multiple entries takes precedence. The only mention of duplicate instances is in the RRULE and EXDATE rules where events exclusions/inclusions overlap. Then duplicate instances are ignore. If it is explicitly written for those items, but NOT for things like DTSTART, then it is difficult to assume duplicate instances are ignored for them as well.

Each of the Components (VEVENT, ...) define which properties can exisit and in what quantity. So multiple DTSTART properties are NOT allowed. -- Brian Suda

Q: Should vCal entitles be represented in XHTML in classes ONLY on block-level element? or should some like VEVENT be block-level and others be of any? does this impact the semantics at all?

A: I don't think the (X)HTML notion of "block-level" should have any bearing whatsoever on vCal entities. You should be able to say

or
and either should work.

Q: Should the transforming application add any additional information to the iCalendar representation other than what was encoded in the HTML? (i.e. UID, the unique identifier might not be present in the HTML code, but could be generated by the transforming application and added to the iCal file. Should this be allowed? or should the transforming app ONLY be allowed to add X-PROPERTY properties?) IF it was not explicitly encoded in the HTML should it be left out? What about default values?

Q: If we are looking at the most semantic way to encoding iCalendar data in HTML then several other attributes should be considered besides just 'class'. There are two other candidated, ID and REL. The ID tag MUST be unique within the XHTML file (this could be used for the UID property). The REL attribute can ONLY be applied to 'a' and 'link' tags, but might be helpful. Are namespac<ETH>H �n option? xml:lang, xml:base, are there any others that might be more semantically correct to encode this data?

Q: To help distinguish xparam values from other actual CSS styles, should we assume/mandate that all values in a class attribute within an encoded iCal component class attribute (<x class="vevent|vtodo|...">) be considered an xparam?

A: If you are using other CSS styles (e.g. "center", "bluebox", "greenline", etc.) nested within an iCal component, those should be avoided and the styles applied to the list of iCal properties instead/also? 

.center, .vevent { text-align: center; }

Q: What about cases where the words "yesterday", "last year", or "last week" was used? How should we represent this? Is this overkill or not appropriate for hcard ? - User:B.K._DeLong

A: I took a stab at "yesterday" and just added a dtstart of the previous day. Not sure how to represent a single year or whole week - User:B.K._DeLong 

<abbr class="dtstart" title="20050114">Yesterday's</abbr>

Recurring Events

Recurring events are tricky. First, there's the question of whether to follow For types with multiple components, use nested elements with class names equivalent to the names of the components a la 

<div class="rrule">every <em class="interval">1</em>
<em class="freq">WEEKLY</em> on <em class="byday">TU</em>
until <em class="until">2004-11-01</em></div>

... or ... 

<abbr class="rrule" title="FREQ=WEEKLY;COUNT=17;INTERVAL=2;BYDAY=TH"> every other
Thursday for 34 weeks</abbr>

... as in Tantek's 1 Aug msg.

DanC has been experimenting with representing his PDA calendar in hCalendar:

  • in palmagent, there's dangerSync.py which uses the XMLRPC interface and spits out RDF data. Then asHCal.xsl converts that to hCalendar
  • then in the RDF Calendar workspace, there's glean-hcal.xsl that turns hCalendar into RDF Calendar, and finally,
  • in SWAP there's toIcal.py that turns RDF Calendar to .ics format.

So I can go from my sidekick to .ics with one Makefile.

events-test.html is a test file that has all the constructs from my PDA data, in hCalendar. In particular, it uses the nested element representation of recurring events. glean-hcal.xsl would be much less fun to write if it had to parse title="FREQ=WEEKLY;COUNT=17;INTERVAL=2;BYDAY=TH".

Then there's the question of "every tuesday afternoon at 2pm Chicago time". This isn't expressible using datetime-design-pattern. There are some good reasons for that, but it leaves a rather large and uncomfortable gap in hCalendar.

Encoding Questions

The way dates are encoded is not always the most user friendly. If i want to encode january 1st, 2005, that is 20050101, which is displayed as 20050101. If we are marking-up comma seperated values, like FN, with each sub-element inside their own tag, then the date should be allowed the same.

(However, FN is in the RFC2426 spec and vCard schema, these individual date terms are not, therefore the reasoning in the last sentence is incorrect. -Tantek) 

20050101
<span class="dtstart"><span class="Year">2005</span><span class="Month">01</span><span class="Day">01</span></span>

With this encoding, then YYYYMMDD schema can be rearranged for different cultures, DD-MM-YYYY for UK, MM-DD-YYYY for US, etc. 

02-01-2005
<span class="dtstart"><span class="Month">02</span>-<span class="Day">01</span>-<span class="Year">2005</span></span>
01-02-2005
<span class="dtstart"><span class="Day" title="first">01</span>-<span class="Month" title="Feb">02</span>-<span class="Year">2005</span></span>

Both of the above encodings are equal, the '-' seperator is ignored by the transforming application. -- Brian Suda

Agreed that the way dates are encoded is not always the most user friendly, but there is an easier solution to this, once you think of what is actually going on in the difference between ISO8601 dates, and dates the way humans use them. Humans typically use an abbrevation or shorthand for a date, like "tomorrow", or "Tuesday", or "the 4th", or perhaps "July 4th". Thus it makes sense to permit this in hCalendar, using the <abbr> tag which provides the ability to markup the human-familiar short form of some data or language, while preserving the long form in the 'title' attribute.

E.g. for the above example of a start date of January 1st, 2005, you could use this markup: 

<abbr class="dtstart" title="20050101">January 1st, 2005</abbr>

Which would display as January 1st, 2005 but would provide the respective ISO8601 date in the title attribute. - Tantek

TO DO

XMDP Profile

Applications

A simple implementation of transforming/extracting vCal data from an XHTML file is available for testing. A bookmarklet is also available. The code will be updated as the spec is finalised. http://suda.co.uk/projects/X2V/ . You may also use http://feeds.technorati.com/events/ for parsing hCalendar events and returning an iCalendar stream.


Parsing

Need to write up an hcalendar-parsing document, similar to hcard-parsing.

Relationships with other microformats

In a Technology Review interview, TBL said "It would have the relationships between the event and the various people chairing it.".

We should have examples of how hCalendar events can indicate such relationships, both in the format and in the presentation.

E.g.: 

* Would it just link to URLs for the various people?  (e.g. to their homepages/blogs etc.)
* Would it include hCards for the various people?  
* Would it link to hCards for various people?
* Perhaps allow all the above?

Mime-Type

According to RFC2445, the proposed media type value is 'text/calendar'.

A standard vCalendar file has an extension of .vcs and MIME type of text/x-vCalendar. If you use iCalendar, the MIME type is "text/Calendar" and the extension is .ics.

Text/X-vCalendar Content Type

The vCalendar object can also be passed as a non-standard MIME media type. This would be useful in order to clearly identify the vCalendar object in an electronic mail message body part. A non-standard, vCalendar object should be identified as the MIME type/subtype "text/x-vCalendar".

@@ - i have to do some more investigation, but (i think) vCalendar is a subset of iCalendar, so many of the same encodings will work for both, but this document is dealing with iCalendar RFC2445 representation!

Button

We need to come up with a nice [ hCal | friendly ] button to indicate that event info on a page/site is using hCalendar. - Tantek.

Possibilities:

  • [ hCal | friendly ]
  • [ hCal | aware ]
  • [ hCal | inside ]
  • [ Valid | hCalendar ] - though that would require writing an hCalendar validator which people could link to.
  • [ <icon> | hCalendar ] where <icon> could be some generic calendar looking thing, or it could be a PHP generated image with the actual date in the icon, kind of like how the Apple iCal icon updates in the dock automatically.

And then we have to pick colors and all that stuff - Tantek.

Other ideas:

  • [ hCal | enabled ]
  • [ hCal | available ] - kind of an off-hand reference to being available for meetings, etc.

- Eric

Including More of iCalendar

Free/Busy information

See Neil Jensen's analysis of how to represent the iCalendar VFREEBUSY object in hCalendar.

In order to show free/busy information, we could either use the existing vevent class (with empty location, summary, etc. properties) or create a new vfreebusy class. We should create a new vfreebusy class because it is consistent with the XHTML design principles, particularly point #4, "Use class names based on names from the original schema...".

In the iCalendar standard, the vfreebusy calendar component frequently has more than one freebusy property, and also may have a number of other properties such as organizer. For example: 

 BEGIN:VFREEBUSY 
 ORGANIZER:jsmith@host.com 
 DTSTART:19980313T141711Z 
 DTEND:19980410T141711Z 
 FREEBUSY:19980314T233000Z/19980315T003000Z 
 FREEBUSY:19980316T153000Z/19980316T163000Z 
 FREEBUSY:19980318T030000Z/19980318T040000Z 
 URL:http://www.host.com/calendar/busytime/jsmith.ifb 
 END:VFREEBUSY

So, our hCalendar representation should include separate elements for the vfreebusy calendar component (defined once) and the freebusy property (possibly defined many times): 

 <span class="vfreebusy"> 
 <span class="freebusy"> 
 <abbr class="dtstart" title="20050721T1000-0800"> 
 July 21, 2005 - 10:00 
 </abbr> - 
 <abbr class="dtend" title="20050721T1100-0800"> 
 11:00 
 </abbr> 
 </span><br/> 
 <span class="freebusy"> 
 <abbr class="dtstart" title="20050722T1000-0800"> 
 July 22, 2005 - 10:00 
 </abbr> - 
 <abbr class="dtend" title="20050722T1100-0800"> 
 11:00 
 </abbr> 
 </span><br/> 
 </span>

According to RFC2445 section 4.8.4.3, "When publishing a "VFREEBUSY" calendar component, the [ORGANIZER] property is used to specify the calendar that the published busy time came from." The organizer property type is CAL-ADDRESS, and can include "non-standard, language, common name and directory entry reference" property parameters. CAL-ADDRESS is "...a URI as defined by [RFC 1738] or any other IANA registered form...".

From what I've seen, Microsoft Outlook typically populates this property with the email address of the calendar owner, which initially made me think of using hCard to specify the organizer. However, given that the property refers to the calendar and not necessarily the person who owns or has published it, I think we should use a new organizer element, as shown below: 

 BEGIN:VFREEBUSY 
 ORGANIZER:jsmith@host.com 
 FREEBUSY:20050314T133000Z/20050314T163000Z 
 END:VFREEBUSY

becomes 

 <span class="vfreebusy"> 
 organizer: <span class="organizer">jsmith@host.com</span> 
 <span class="freebusy"> 
 <abbr class="dtstart" title="20050314T133000Z"> 
 March 14, 2005 - 13:30 
 </abbr> - 
 <abbr class="dtend" title="20050314T163000Z"> 
 16:30 
 </abbr> 
 </span><br/> 
 </span>

Hmmm, this looks a little funny when the organizer is so obviously an email address, but at least it is semantically correct. The other problem that I can now see occurring is when the organizer property has parameters, for example (from the iCalendar spec): 

 ORGANIZER;CN=JohnSmith;DIR="ldap://host.com:6666/o=3DDC%20Associ 
  ates,c=3DUS??(cn=3DJohn%20Smith)":MAILTO:jsmith@host1.com

Perhaps it's best to use the same approach described in "Human vs. ISO8601 dates problem solved"; use the abbr element like so: 

 <span class="vfreebusy"> 
 <span class="freebusy"> 
 organizer: <abbr class="organizer" title="CN=JohnSmith;DIR=ldap://host.com:6666/o=3DDC%20Associ 
 ates,c=3DUS??(cn=3DJohn%20Smith):MAILTO:jsmith@host1.com">jsmith@host1.com</abbr> 
 <abbr class="dtstart" title="20050314T133000Z"> 
 March 14, 2005 - 13:30 
 </abbr> - 
 <abbr class="dtend" title="20050314T163000Z"> 
 16:30 
 </abbr> 
 </span> 
 </span>

A different reading, particularly of section 4.6.4 "Free/Busy Component", is that the organizer property refers to a calendar user, not the calendar itself. In that section we find this: "When used to publish busy time, the "ORGANIZER" property specifies the calendar user associated with the published busy time".

Under this reading, an hCard might be appropriate. But if for some reason a simpler representation is wanted, using an <a> tag instead of <span> or <abbr> is closer semantically, more consistent with expected web presentation of uri-type data, and easily handles the ORGANIZER examples in the RFC. For example: 

     ORGANIZER;CN="John Smith":MAILTO:jsmith@host.com

becomes 

     <a class="organizer" href="mailto:jsmith@host.com">John Smith</a>

and 

 ORGANIZER;CN=JohnSmith;DIR="ldap://host.com:6666/o=3DDC%20Associ 
  ates,c=3DUS??(cn=3DJohn%20Smith)":MAILTO:jsmith@host1.com

becomes 

     <a class="organizer" href="mailto:jsmith@host.com" 
title="DIR=ldap://host.com:6666/o=3DDC%20Associates,c=3DUS??(cn=3DJohn%20Smith)">John Smith</a>

To-Do information

The Policy Aware Web (PAW) Project Meeting - 23 Aug 2005 uses class="vtodo" to capture action items. Clearly recording action items from a meeting and publishing them as minutes is a good practical example use of the VTODO object on the web.

What's the scenario for usage though?

What kind of indexer/aggregator application would find these VTODO items and what would it do with them?

Perhaps with some way of figuring out who the to-do item is assigned to ("ATTENDEE"), who assigned it ("DELEGATED-FROM"), and a whitelisting of who, perhaps the "ORGANIZER" property, (and their domains/URLs) that a user would accept assignments from, a user could aggregate to-do items assigned from other folks. Then question remains how to update the status ("STATUS") (RFC 2445 4.8.1.11 Status) on that to-do item when it is (a) completed ("COMPLETED"), (b) abandoned/cut/rejected ("CANCELLED"), (c) some progress is made ("IN-PROCESS") etc. There certainly seems to be sufficient expressiveness in VTODO and its properties to do a decentralized to-do list / task distribution system. Could be very interesting for helping open source projects and other distributed teams do project management using the Web.

References

Normative References

Informative References

Other Implementations/Ideas

Blogs About Calendaring
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