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Re: Subjects as Literals

From: Hugh Glaser <hg@ecs.soton.ac.uk>
Date: Mon, 5 Jul 2010 22:40:00 +0000
To: Sampo Syreeni <decoy@iki.fi>
CC: David Booth <david@dbooth.org>, Kingsley Idehen <kidehen@openlinksw.com>, "nathan@webr3.org" <nathan@webr3.org>, Pat Hayes <phayes@ihmc.us>, Toby Inkster <tai@g5n.co.uk>, Dan Brickley <danbri@danbri.org>, Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
Message-ID: <EMEW3|6aadd1861358c42f5e9a74b339fd80dam64NeV02hg|ecs.soton.ac.uk|C8581DD0.159FC%hg@ecs.soton.ac.uk>
Hi Sampo.
I venture in again...
I have much enjoyed the interchanges, and they have illuminated a number of
cultural differences for me, which have helped me understand why some people
have disagree with things that seem clear to me.
A particular problem in this realm has been characterised as
S-P-O v. O-R-O and I suspect that this reflects a Semantic Web/Linked Data
cultural difference, although the alignment will not be perfect.
I see I am clearly in the latter camp.
Some responses below.


On 05/07/2010 19:36, "Sampo Syreeni" <decoy@iki.fi> wrote:

> On 2010-06-30, Hugh Glaser wrote:
> 
>> RDF permits anyone to say anything about anything . . . except a
>> literal if it is the subject of the property you want to use for the
>> description.
> 
> The way I see it, the main reason for this restriction is that the data
> is supposed to be machine processable. Literals rarely are, especially
> in their original, plain form. I mean, suppose we allowed literals as
> subject, predicate and object. What does it really mean if I say
> "Sally"@en "likes"@en "Mike"@en?
> 
> I'd argue pretty much nothing processable. That's because literals tack
> on an arbitrary, limited number of type specifiers (type and perhaps
> language) to textual data, and neglect everything beyond that. That is
> not how full disambiguation is done; it's how a human processor
> *minimally* disambiguates a piece of text, without making it
> unambiguous.
> 
> With Schema derived or otherwise strictly derived types, the level of
> disambiguation can be the same as or even better than with URI's, true.
> But then that goes the other way around, too: URI's could take the place
> of any such precise type. Beyond that, all that literals do is invite
> people to import more ambiguity into the RDF/SemWeb framework.
> 
> So, better to limit that to the object, in case we just *have* to have
> it somewhere. (I'd rather do without entirely.)
You see this as a problem of having a literal in the "subject" position.
I might equally decide it is a problem with having literal in the "object"
position.
Literals are literals wherever they appear - they have no deeper semantics,
and they certainly do not identify anything other than the literal that they
are, if that makes sense.
> 
>> So I can say: foo:booth isNamed "David Booth" But of course I can't
>> say: "David Booth" isNameOf foo:booth
> 
> You can say the same thing, as you pointed out. So you're aiming at
> grammatical symmetry in excess of expressive capability. Why? There is
> definite value in making the relation asymmetric: that way you can be
> surer that what is being talked about stays...the subject. It's not by
> any means sure that that is really going to be useful, no.
Ah, perhaps the nub.
The "subject" is no more the thing "being talked about" than the "object".
I am not asking for symmetry of the grammar, if I understand what you mean.
I am asking for the freedom to express the statements I want in the way I
want, so that I can query the way I want.
At the risk of repeating myself:
If someone wants to say "666" foo:isTheNumberOf bar:theBeast
and I have to tell them (as I do) ah, you can't say that, you need to
introduce a resource numbers:666 rdfs:label "666". ...
or  bar:theBeast foo:hasNumber "666"
I actually feel pretty stupid, having told them that RDF represents
relations in a natural and basic way.
In fact, I always feel a bit embarrassed when I get to the bit in my slides
that shows there are two sorts of triples, as I have just said that the
triples are just a directed graph.
> 
> But at the same time it's perfectly sure that you would have to start
> employing triples with both the subject and the object a literal, before
> the current model can constrain you semantically. That'd then be pretty
> extreme: the precise semantics of literals are tricky enough as they
> stand. Pretty much the only genuine use cases I can come up with
> off-hand are explicit unit conversions and label translations -- and
> then anything that goes that far should probably get URI's and/or
> epi-RDF conversion code in the first place. After all, both scenarios
> also call for context, which might have to be disambiguated beyond
> mere lexical form and type. (E.g. homologues or units with identical
> dimensions but different usage.)
I think you might be sort of agreeing here, but I don't understand all this
discussion of context that has been going on.
People seem to be somehow assuming that a literal in position one implies
more "context" than one in position three, which seems strange to me.
I guess that is because I am O-R-O, not S-P-O.

All that being said, I am still worried about the costs of any change,
compared to value returned.
Although some recent posts have suggested that it is not such a bad thing.

Best
Hugh
Received on Monday, 5 July 2010 22:41:43 UTC

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