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Re: draft of LC comment to XML Schema WG

From: Ian Horrocks <ian.horrocks@comlab.ox.ac.uk>
Date: Mon, 4 Aug 2008 17:33:46 +0100
Message-Id: <DFF1151A-CE04-4402-A50E-09A8BA45749B@comlab.ox.ac.uk>
Cc: public-owl-wg@w3.org
To: Peter F. Patel-Schneider <pfps@research.bell-labs.com>

On 29 Jul 2008, at 17:15, Peter F. Patel-Schneider wrote:

>
> Here is my proposed LC comment to the XML Schema WG concerning  
> datetime.
> I have some comments in [].  I did not "ask" for changes to dateTime
> itself, aside from a new derived datatype, but instead put forward  
> what
> I think are our concerns.
>
> peter

Looks good. I did have a few comments/suggestions though -- they are  
in line below.

Thanks,
Ian


>
>
>
>
> The W3C OWL WG is determining how to use XML Schema dateTime values  
> from
> the last call working draft http://www.w3.org/TR/xmlschema11-2/ in OWL
> ontologies.  The main problem we face concerns dealing with dateTime
> values that do not have a timezone.  The document puts these values  
> on a
> single separate timeline that is partially ordered with respect to the
> absolute timeline.
>
> For the purposes of reasoning in OWL, it is much easier to deal with
> dateTime values where the timezone is present.  Such values can be
> converted to single time points (using timeOnTimeline) and a complete
> order determined from the time points.  We would thus like to have a
> derived XML Schema datatype for dateTime with a required timezone.  [I
> added this last sentence based on some evidence but the WG should
> confirm.]
>
> There are already OWL ontologies that contain dateTime values where  
> the
> timezone is absent.  Such dateTime values may come from different
> documents, and that really have a different notion of what their local
> (unspecified) time is.  The document,

You refer to "the document" several times. I assume this is http:// 
www.w3.org/TR/xmlschema11-2/. Wouldn't it be clearer to cite this in  
the usual way:

[1] http://www.w3.org/TR/xmlschema11-2/

and use "[1]" instead of "the document"?

> however, makes these values all
> equal.
>
> Our proposed solution to handling such ontologies is to put off the  
> task
> of determining "missing" timezones to tools, with roughly the wording
> that tools MAY accept dateTime values with an absent timezone by
> determining what the "local" timezone is for the value and SHOULD
> produce a warning if they do so; otherwise dateTime values with  
> missing
> timezone are syntax errors.

I liked Sandro's suggested refinement here.

>
> This treatment of dateTime values appears to violate the document, as
> different dateTime values that compare equal according to the document
> are turned into dateTime values that do not compare equal.  The WG  
> would
> appreciate guidance on how to do this processing in a compliant  
> manner.

I don't really see how this violates [1] any more than it violates  
the OWL spec -- tools may change time values in an ontology in a way  
that could be interpreted as being in violation of [1], but from an  
OWL point of view we *only* compare values with a timezone in a way  
that is compliant with [1].

>
> There are other potential solutions to reasoning with such dateTime
> values (such as treating them as true intervals).  However, these
> solutions also appear to violate the document.

I'm not sure if we need this either (for the same reason) -- what are  
we suggesting/asking?

>
>
> We also do not find a justification for having the range of  
> timezone be
> -840 to +840.  The range of timezones currently in use ranges from
> UTC-12 to UTC+14 (http://en.wikipedia.org/wiki/List_of_time_zones).
> [This last is also an extrapolation from some evidence at the F2F.]
>
Received on Monday, 4 August 2008 16:34:22 GMT

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