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Revision as of 21:32, 19 August 2005 by RobertBachmann (talk | contribs) (typo)
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This page is a draft.

This is a page for exploring a datetime design pattern.

The pattern which is now used in hCalendar and hReview is something like this:

<abbr class="foo" title="YYYYMMDDTHH:MM:SS+ZZZZ">Date Time</abbr>

where foo is the semantic classname which is being applied to this date/time, the title of the <abbr> is an ISO 8601 date/time and "Date Time" is a human-friendly representation of the same date/time.

This pattern is likely to be highly resuable.


Can this not be viewed as a microformat in itself?


It could, but inventing a microformat for the sake of inventing a microformat is against the microformat principles. If there is a specific real world problem (and uses cases) that such an elemental microformat would solve, then it would be worth considering.

Until then it is best to keep the <abbr> datetime concept merely as a microformat design pattern, to be used in _actual_ microformats that have a demonstrated practical need.

-- Tantek

Excerpt from #microformats Aug 18th. Please edit!

Aug 18 15:16:14 <Tantek>	DanC, what do you think of RFC3339?
Aug 18 15:17:14 <Tantek>	ISO8601 subset
Aug 18 15:17:19 <DanC>	Date and Time on the Internet: Timestamps
Aug 18 15:17:30 <DanC>	Klyne is a good guy. I wonder if I talked with him about this.
Aug 18 15:17:32 <Tantek>	compat with W3C-NOTE-DATETIME
Aug 18 15:17:50 <Tantek>	compat with xsd:dateTime
Aug 18 15:17:57 <Tantek>	it's a strict intersection subset
Aug 18 15:17:59 <DanC>	I consider W3C-NOTE-DATETIME obsoleted by XML Schema datatype-- yeah.. xsd:dateTime
Aug 18 15:18:32 <Tantek>	compare/contrast normatively using xsd:dateTime vs. RFC3339
Aug 18 15:18:41 <Tantek>	note: Atom 1.0 chose RFC3339
Aug 18 15:18:50 <Tantek>	i would like input from the microformats community on this
Aug 18 15:19:27 <DanC>	in what context are you evaluating RFC 3339?
Aug 18 15:19:28 <jcgregorio>
Aug 18 15:21:24 <DanC>	which microformat is the question coming from, Tantek ?
Aug 18 15:23:31 <DanC>	"   The grammar element time-second may have the value "60" at the end of
Aug 18 15:23:31 <DanC>	   months in which a leap second occurs" The XML Schema WG is in the 27th level of leap-second-hell for the past few months, I gather.
Aug 18 15:24:21 <DanC>	yeah... here's the scary bit: "   Leap seconds cannot be predicted far into the future.  The
Aug 18 15:24:21 <DanC>	   International Earth Rotation Service publishes bulletins [IERS] that
Aug 18 15:24:21 <DanC>	   announce leap seconds with a few weeks' warning."
Aug 18 15:26:03 <Tantek>	DanC, which microformats? any/all that use datetime fields.
Aug 18 15:26:36 <DanC>	hard to give useful advice, then.
Aug 18 15:26:58 <DanC>	I expect they'll use datetime fields for different things that have different cost/benefit trade-offs
Aug 18 15:27:26 <DanC>	do you know of any particular differences that matter to anybody?
Aug 18 15:56:43 <KragenSitaker>	RFC3339 suggests -07:00, which seems like an improvement over -0700 anyway
Aug 18 15:56:49 <Tantek>	Kragen, agreed
Aug 18 15:57:01 <Tantek>	RFC3339 is certainly preferable to the ISO8601 subset in iCalendar
Aug 18 16:05:57 <DanC>	Tantek's right, Kragen; iCalendar looks like it solves the local timezone problem but doesn't.
Aug 18 16:06:14 <DanC>	and it's true that there's no standard solution to the local timezone problem
Aug 18 16:06:39 <Tantek>	so instead of appearing to solve the problem but not solving it, we chose to provide the ability to *approximate* the local timezone using e.g. "-07:00"
Aug 18 16:06:49 <DanC>	the simplest thing is to have people use Z time in hCalendar. But I gather that's unacceptably unusable?
Aug 18 16:07:35 <Tantek>	DanC, yes, the simplest thing is to have everyone use UTC Z
Aug 18 16:07:38 <Tantek>	However
Aug 18 16:07:50 <Tantek>	it is not *nearly* as usuable/verifiable
Aug 18 16:07:55 <Tantek>	as -07:00 etc.
Aug 18 16:08:02 <Tantek>	hence the decision to go with the latter
Aug 18 16:08:12 <Tantek>	some degree of human verifiability is important here
Aug 18 16:14:21 <Tantek>	DanC, my perception is that RFC3339 is a subset
Aug 18 16:17:00 <DanC>	   time-numoffset  = ("+" / "-") time-hour ":" time-minute
Aug 18 16:17:34 <DanC>	ok, then I can't see any differences. (modulo recent leap seconds issues that may affect xsd:dateTime )
Aug 18 16:18:07 <Tantek>	would be interesting to know why Atom 1.0 chose RFC3339 over xsd:dateTime
Aug 18 16:18:21 <Tantek>	if there was a "real" reason or if it was arbitrary / coin-flip.
Aug 18 16:18:43 <KragenSitaker>	rfc3339 is pretty short.
Aug 18 16:19:36 <Tantek>	DanC, BTW, which came first? REC for xsd:dateTime or RFC3339?
Aug 18 16:19:50 <DanC>	RFC3339 is dated July 2002 ...
Aug 18 16:19:54 <KragenSitaker>	Right --- and you might be able to understand xsd:dateTime without reading all of xml schema, you wouldn't be confident of it
Aug 18 16:20:25 <DanC>	W3C Recommendation 28 October 2004 ... but that's 2nd ed...
Aug 18 16:20:47 <DanC>	W3C Recommendation 02 May 2001
Aug 18 16:22:10 <DanC>	I don't see a BNF in ...
Aug 18 16:22:43 <KragenSitaker>	yeah, appendix D of the current xml schema datatypes document seems a little scanty, actually
Aug 18 16:23:28 <DanC>	ah... 2nd ed of is much more explicit about syntax.
Aug 18 16:23:30 <KragenSitaker>	it's 1100 words but still doesn't give any examples
Aug 18 16:23:35 <DanC>	still, it's given in prose and not BNF
Aug 18 16:24:17 <KragenSitaker>	sections 3.2.9 through 3.2.14 seem to be the relevant ones around #date
Aug 18 16:24:29 <KragenSitaker>	which is another 2200 words
Aug 18 16:24:42 <DanC>	wow... they changed the canonical form of date from always-Z to timezone-allowed between 1st edition and 2nd edition
Aug 18 16:25:01 <Tantek>	Kragen, DanC, these are very good analyses
Aug 18 16:25:21 <Tantek>	could I ask you to summarize the pros/cons for each in a new section at end of
Aug 18 16:25:22 <Tantek>	?
Aug 18 16:25:58 <KragenSitaker>	rfc 3339 is 4000 words, excluding the last two pages of boilerplate.
Aug 18 16:26:31 <KragenSitaker>	so it's actually longer than the datetime-relevant parts of XSD but it seems much more rigorous and clear
Aug 18 16:28:37 <DanC>	my advice is: normatively cite both, and claim they specify the same syntax, and let anybody who discovers otherwise send you a bug report with a test case
Aug 18 16:29:12 <KragenSitaker>	danc: nice hack

The RFC3339 has a mandatory TIME portion of the DATE-TIME. Some vCard/iCalendar DATE-TIME stamps can omit the TIME. For instance, DTSTART, if that is a full day event, then you can omit the time. BDAY in vCard can be respresented by only a DATE. I like the idea of restricting the possible date formats, but i think that TIME should be optional, which it isn't in RFC3339. - brian suda

RFC 3339 allows lowercase 't' and 'z' while XSD doesn't. Specifying RFC 3339 plus 'T' and 'Z' MUST be caps will make them the same. - Joe Gregorio