datetime-design-pattern
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.
--RyanKing
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 http://www.ietf.org/rfc/rfc3339.txt
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> http://bitworking.org/news/Date_Constructs_in_the_Atom_Syndication_Format
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 http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#dateTime ...
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 http://www.w3.org/TR/xmlschema-2/#date 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 http://microformats.org/wiki/datetime-design-pattern
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