This page is a draft.
Datetime Design Pattern
This is a page for exploring a datetime design pattern.
- Use the Datetime Design Pattern to make datetimes that are human readable also formally machine readable.
- This design pattern arose as a result of solving the practical need for human readable dates for hCalendar.
How to use it
- enclose the human-friendly datetime that you want to make machine readable with
- as per the class-design-pattern, add the appropriate
classattribute to the
- add a
titleattribute to the
abbrelement with the machine readable ISO8601 datetime or date as the value
<abbr class="foo" title="YYYY-MM-DDTHH:MM:SS+ZZ:ZZ">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.
Profile of ISO8601
We recommend that any microformat using the date-time-design pattern use a profile of ISO8601. There are currently two widely used profiles which SHOULD be reused.
- RFC 3339
- W3C Note on Datetimes
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.
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.
Here's an exhaustive comparison from ndw. I think xsd:dateTime also allows unqualified local times, while RFC3339 allows only UTC with no known timezone (-00:00). In the end, Atompub followed the advice of Sam Ruby and Scott Hollenbeck, our area director. Atom dates make some additional restrictions on RFC3339, such as uppercase T and Z characters for compatibility with xsd:dateTime, RFC3339, W3C-DTF, and ISO8601. --Robert Sayre
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
The following regular expression (parsed VERBOSE) should break apart a datetime and cover many lightly broken cases seen in the wild. This has been tested under Python.
^ (?P<year>\d\d\d\d) ([-])?(?P<month>\d\d) ([-])?(?P<day>\d\d) ( (T|\s+) (?P<hour>\d\d) ( ([:])?(?P<minute>\d\d) ( ([:])?(?P<second>\d\d) ( ([.])?(?P<fraction>\d+) )? )? )? )? ( (?P<tzzulu>Z) | (?P<tzoffset>[-+]) (?P<tzhour>\d\d) ([:])?(?P<tzminute>\d\d) )? $