RE: status of xsd:duration in OWL (and RIF and SPARQL) - ACTION-164: RDF WG

I definitely have something else to do right now but I'll have a look.

And yes, I now time and duration are not as simple as they are but they can be contextually contained within a particular domain of application (beyond relativity ;--).

I'll have another look.

PS: still don't have a nice example for my simple time representation :--(

From: Bijan Parsia [mailto:bparsia@cs.man.ac.uk]
Sent: mardi, 8. mai 2012 11:36
To: Evain, Jean-Pierre
Cc: 'Michael Schneider'; 'Ivan Herman'; Ian Horrocks; public-owl-wg@w3.org; Public-Rif-Wg (E-mail); Peter F. Patel-Schneider; Sandro Hawke
Subject: Re: status of xsd:duration in OWL (and RIF and SPARQL) - ACTION-164: RDF WG

Just a quick hit and then I really must prep for class. (Thanks to Ivan for the diff...it's pretty useful.)

On 8 May 2012, at 10:18, Evain, Jean-Pierre wrote:


Dear Michael,

I appreciate your time and effort in trying to bring more background around the current situation.

I must say that I am growingly puzzled. This is definitely making me question my resolution to move for these technologies.

The problem really generally is in XSD.

[snip]
I believe that the semantics of time, date and duration are clear

This is definitely a false belief. Simple reflection on calendars should show that. That's not to say that we can't come up with something useful, but the history of computing (and of science) is littered with problematic representations of time (generally speaking).


and I am surprised that they may be considered as being not mathematically univocally representable.

Relativity theory has a few things to say about that :) (Seriously, identity of time instants or durations is non trivial.)

In any case, we're not talking about representations in general, but the particular representations given by XSD 1.1. They need to be well defined enough and *properly* defined enough to not cause problems and be useful.
[snip]
Why not simply reuse the xsd datatypes? That would solve all the above problems with a simple expression in a well defined format. What do I miss?
[snip]

That the XSD datatypes are not as nice as you presume. Seriously. Just look at the comparison critera for Duration:
            http://www.w3.org/TR/xmlschema11-2/#duration

It's not, "Represent as an integer number of seconds, and then use integer comparison", it's "add them to some magic constants and":
            "If all four resulting dateTime value pairs are ordered the same way (less than, equal, or greater than), then the original pair of durationvalues is ordered the same way; otherwise the original pair is *incomparable*."

Now it also claims that:
            "Under the definition just given, two duration<http://www.w3.org/TR/xmlschema11-2/#duration> values are equal if and only if they are identical."
Which is promising.


I hope this makes it clear that "just reusing" xsd:duration requires significant effort.


Cheers,
Bijan.


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