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Re: Issue 80: terminology

From: Michael Kifer <kifer@cs.sunysb.edu>
Date: Thu, 26 Mar 2009 14:31:27 -0400
To: Chris Welty <cawelty@gmail.com>
Cc: RIF WG <public-rif-wg@w3.org>
Message-ID: <20090326143127.29761f48@kiferserv>


On Thu, 26 Mar 2009 06:29:24 -0400
Chris Welty <cawelty@gmail.com> wrote:

> 
> Great- let's try to resolve this at the upcoming Telecon. Would anyone  
> object to a resolution to add literal-not-identical to dtb?

I think I am ok with it, but to be sure it would be useful if the proposal were
spelled out explicitly, without pointers to other emails.

michael


> One point of ambiguity remains I think: is lni(?x,?y) true if ?x and?y  
> are both literals but of different types, or do ?x and ?y have to be  
> of the same type (but different values) for the pred to be true?
> 
> Truth table for Lni(?x,?y):
> ?x and?y are literals of the same type and the same value in the value  
> space: FALSE
> ?x and ?Y are literals of the same type and different values in the  
> vspace: TRUE
> ?x and ?y are literals of different types:
> ?x or ?y is a non-literal: FALSE
> 
> 
> -Chris (sent from my iPhone)
> 
> On Mar 26, 2009, at 5:59 AM, Jos de Bruijn <debruijn@inf.unibz.it>  
> wrote:
> 
> > I guess many people do feel having literal-non-identity is important  
> > in
> > RIF.  So, let's go for option (1) from [4], i.e., we have
> > literal-non-identity and we have the individual (in)equality operators
> > based on the XPath operators.
> >
> >
> > Jos
> >
> > Dave Reynolds wrote:
> >> We had a useful but not fully conclusive discussion on this at the  
> >> last
> >> telecon and tried to clarify our terminology. I felt afterwards we
> >> didn't quite have it right so here's an attempt to articulate that.
> >>
> >> There are actually three notions of "equality" buried in here.
> >>
> >> (1) Identity. Two literals are identical if they correspond to the  
> >> same
> >> value in the value space.
> >>
> >> (2) Equality. XSD defines algorithms for equality which mean that two
> >> non-identical points in a given value space can be equal. However,  
> >> for
> >> XSD this equality is restricted to be within a datatype[1] and so
> >> doesn't include the "1"^^xsd:int = "1.0"^^xsd:float case.
> >>
> >> (3) Equivalence[3]. XPath F&0 defines equality operators (a different
> >> notion from the mathematical equality functions which characterize  
> >> the
> >> XSD value spaces). These can span multiple datatypes, specifically
> >> numeric-equal does.  This is the one that does type promotion and
> >> permits "1"^^xsd:int = "1.0"^^xsd:float.
> >>
> >>
> >> Now, in XML Schema 1.0, which is the version we current reference in
> >> DTB, equality and identity are the same[2]. So the issues we were
> >> worrying about in the telecon don't apply.
> >>
> >> In XML Schema 1.1 some datatypes have a non-identity equality.
> >> Specifically xsd:dateTime and float/double. Though with float/ 
> >> double the
> >> exceptions (-0 = +0, Nan != NaN) are perhaps not so interesting.
> >>
> >> For OWL then they define xsd:dateTimeStamp to have a value space
> >> corresponding to a timeline instead of following the XML Schema 1.1
> >> structural model and so for OWL's definition identity and equality
> >> coincide again.
> >>
> >> So my contention is that the way literal-not-equal is defined in  
> >> DTB at
> >> present (non-identity) corresponds to the equality notion in OWL  
> >> for all
> >> the relevant datatypes and I keep my preference for options 2 or 1  
> >> [4].
> >>
> >> This contention is trivially true if we stick to XML Schema 1.0  
> >> because
> >> there is no distinction between equality and identity there. If we  
> >> move
> >> to XML Schema 1.1 (is there a proposal to do this? I assume so) there
> >> are differences but the main problematic datatype is not included in
> >> OWL[5].
> >>
> >> Dave
> >>
> >> [1] http://www.w3.org/TR/xmlschema11-2/#value-space
> >> "For purposes of this specification, the value spaces of primitive
> >> datatypes are disjoint, even in cases where the abstractions they
> >> represent might be thought of as having values in common."
> >>
> >> [2] http://www.w3.org/TR/xmlschema11-2/#value-space
> >> "Note: In the prior version of this specification (1.0), equality was
> >> always identity.  This has been changed to permit the datatypes  
> >> defined
> >> herein to more closely match the "real world" datatypes for which  
> >> they
> >> are intended to be used as transmission formats."
> >>
> >> [3] I don't know what a good name for this is so I'm using  
> >> "equivalence"
> >> for now. You could call it "programmatic equality" or "pragmatic
> >> equality" or something.
> >>
> >> [4] http://lists.w3.org/Archives/Public/public-rif-wg/2009Mar/0076.html
> >>
> >> [5] OK, that does leave the corner cases of float/double (-0 = +0,  
> >> Nan
> >> != NaN) I haven't checked how OWL handle these. If those are the only
> >> differences then I personally don't care either way.
> >
> > -- 
> > +43 1 58801 18470        debruijn@inf.unibz.it
> >
> > Jos de Bruijn,        http://www.debruijn.net/
> > ----------------------------------------------
> > Many would be cowards if they had courage
> > enough.
> >  - Thomas Fuller
> >
> 
> 
Received on Thursday, 26 March 2009 18:32:08 GMT

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