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RE: DAML+OIL: Questions & Improvements.

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Tue, 30 Jan 2001 12:16:36 +0000 (GMT)
Message-ID: <14966.45220.650820.250320@galahad.cs.man.ac.uk>
To: Dan Brickley <danbri@w3.org>
Cc: "King . Dany" <DKing@drc.com>, "'www-rdf-logic'" <www-rdf-logic@w3.org>
On January 30, Dan Brickley writes:
> 
> hi Ian,
> 
> On Tue, 30 Jan 2001, Ian Horrocks wrote:
> 
> > On January 29, Dan Brickley writes:
> > >
> > > On Mon, 29 Jan 2001, Ian Horrocks wrote:
> > >
> > > > > Syntactically however, it is... mostly (discrepancies: 1. RDF is requires
> > > > > acyclic subclass relations, DAML+OIL allows cyclic subclass relations; 2.
> > > > > DAML+OIL requires one syntax for cardinality to avoid exposed content, thus
> > > > > other equivalent and legal RDF syntaxes are illegal for DAML+OIL
> > > > > cardinality; 3. RDF allows only one range restriction per property, DAML+OIL
> > > > > allows multiple; 4. the "daml:collection" doesn't exist in RDF).
> > > >
> > > > 1 and 3 are likely to change in RDFS.
> > >
> > > Ahem! Pointer please to evidence for claim (1). Or a PaperTrail
> > > (http://www.w3.org/DesignIssues/PaperTrail).
> > >
> > > Regarding (3), my inclination is to agree (and also fix rdfs:domain). The
> > > important thing with domain/range is to define what they mean, not how
> > > many times one can write down statements using them. The RDFS prose gets
> > > this wrong imho.
> 
> I agree. As an editor I can't change this without RDF working group sayso.
> We don't currently have an RDF working group, but I expect that situation
> to change shortly. Watch this space...
> 
> >

Dan,

My arguments about the removal of the subClassOf cycles restriction
were not intended be taken seriously (well, not completely
seriously). Sorry for any confusion.

Ian

> > There have been extensive discussions about (3) on the RDF list(s),
> > w.r.t. both range and domain, most/all of which led to the conclusion
> > that the original specification was a mistake and should be
> > changed. My claim regarding (1) is rather more doubtful. The evidence
> > is as follows:
> >
> > a) I spoke to Ora Lassila about it and he didn't raise any strong
> > objections.
> 
> <shrugs/>
> 
> Ora didn't raise any strong objections to the contrary position at the
> time either. As I remember (RDFS WG mail archive search seems broken
> currently) the decision regarding subclass cycles was explicitly brought
> to Guha and Ora's attention (as our resident KR gurus), and it got their
> OK. I originally proposed that we used reciprocal sub-class relations
> between classes as an idiom for representing class synonymy. This led to
> discussion of subclass loops, the decision to exclude them and thereby
> punt 'class synonymy' off to future RDF working groups. Others may
> remember this differently!
> 
> The cycles thing could've gone either way. I can't profess a strong view
> on this, except to note that "likely to change" is a rather concrete
> claim. If only we make make a W3C REC from everything Ora didn't "raise
> strong objections to" the Web might be a more interesting place... ;)
> 
> > b) The restriction is clearly senseless, so it is bound to be dropped
> > eventually.
> 
> You're sounding more and more like TimBL! There are a world of reasons
> beyond the purely mathematical for making this kind of design decision.
> We might for eg consider the usability angle. RDF, DAMLOIL and the like
> are already rather tough for mainstream Web developers to get their heads
> around. Even though subclass cycles are not mathematically problematic, I
> suspect you'll agree they're a little counterintuitive for folk from non
> KR/math backgrounds. Similarly, the ability to generate a decent user
> interface from schema information is important; tree widgets are plentiful
> and a common UI metaphor; general graph viewers are less readily
> available and less well known.
> 
> But I don't want to overstate my case. I'd be happy to see this constraint
> lifted. I'd be slightly happier to see the RDF-Logic community define some
> utility relations for class synonymy and the like, rather than overload
> the sub-class relation with this work. But either would do.
> 
> BTW I wouldn't take "this is kinda dumb; therefore it will doubtless be
> fixed" as a guiding rule for predicting Internet standards evolution.
> Hopefully that'll be the case with domain/range. I'm yet to be persuaded
> re sub-class loops, though I'm inclined to believe whatever Ora says on this :)
> 
> dan
> 
> -- 
> mailto:danbri@w3.org
> 
Received on Tuesday, 30 January 2001 07:08:16 GMT

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