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RE: An approach to xsd:dateTime

From: Boris Motik <boris.motik@comlab.ox.ac.uk>
Date: Wed, 23 Jul 2008 18:14:26 -0400
To: "'Michael Smith'" <msmith@clarkparsia.com>, <public-owl-wg@w3.org>
Message-ID: <000001c8ed11$7a6a1a60$4f744381@wolf>


The problem seems a bit more complicated. What do you do with the time zone if it is present on some constant?

Another way forward would be to make the value space of dateTime the (continuous) time line at Greenwich. Each number on the time
line would correspond to the number of seconds elapsed from some fixed point, such as the beginning of AD or something similar. (I
am deliberately not using UTC -- I'll explain shortly.) In this way, you have a unique time point for every event, and that time
point is not dependent on the time zone or on effects such as daylight saving. Furthermore, the value space is isomorphic to
owl:number, which makes reasoning simpler.

Time zone, daylight saving, and leap seconds would be relevant only for dateTime constants. For example, you might have a constant
"midnight on 1/1/2008 in London", and this constant would be mapped to the same time point as the constant "1am on 1/1/2008 in
Berlin". Thus, the time zone, leap seconds, and daylight saving would be relevant only when you want to refer to actual time points.

Now I deliberately didn't want to say that the value space of dateTime should be UTC because UTC time consists of a day, month,
year, hour, minute, and second. As such, it is not just one number, but six numbers, which makes reasoning more complicated.
Furthermore, a minute in UTC can contain leap seconds, which is yet another complication for reasoning. 

I believe that such a design would work. The main problem, however, is that we don't have (or at least I don't know of) a standard
that we can point to and that we could reuse. Specifying something like this from scratch might require a lot of work; furthermore,
I don't believe that this is the core competence of our WG.



> -----Original Message-----
> From: public-owl-wg-request@w3.org [mailto:public-owl-wg-request@w3.org] On Behalf Of Michael Smith
> Sent: 23 July 2008 17:33
> To: public-owl-wg
> Subject: Re: An approach to xsd:dateTime
> On Wed, 2008-07-23 at 14:49 -0400, Michael Smith wrote:
> > As I read the XML Schema 1.1 description of dateTime [1], the primary
> > problem it presents as a datatype is that timezone is optional.  If OWL
> > were to require the timezone property, all values map to a single point
> > on a discrete number line (see [2]), making implementation equivalent to
> > implementation of xsd:integer.
> Tracker, this was in reference to ISSUE-126.
> --
> Mike Smith
> Clark & Parsia
Received on Wednesday, 23 July 2008 22:16:09 UTC

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