Re: Subjects as Literals

On 6 Jul 2010, at 09:19, Dan Brickley wrote:

> On Tue, Jul 6, 2010 at 12:40 AM, Hugh Glaser <hg@ecs.soton.ac.uk> wrote:
>> 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.
> 
> 
> imho RDF processing requires both perspectives, and neither is more
> semwebby or linky than the other.

I agree with what you say here Dan, though I don't think it has anything
to do with S-P-O or O-R-O.

That we have different graphs and that they can be merged are furthermore
complimentary and essential to the semantic web. The RDF Semantics in my
view clearly contains the notions of separate graphs, since it shows how
they should be merged when *both are considered to be True*! Therefore 
if two graphs are not considered to be true there is no requirement to
merge them. This is quite clear in the talk of possible worlds from the RDF Semantics document

[[
The basic intuition of model-theoretic semantics is that asserting a sentence makes a claim about the world: it is another way of saying that the world is, in fact, so arranged as to be an interpretation which makes the sentence true. In other words, an assertion amounts to stating aconstraint on the possible ways the world might be. 
]]

( In this way of thinking about things relations are thought of as sentences. So this is just one more way of thinking of the relations in addition to S-P-O or O-R-O)

Now it is quite clear from the above that when one has two incompatible graphs, then both of them still have meaning. They both can describe possible ways the world can be. It is just that merging them will lead to the set of all possible worlds: ie, nothing will be said. 

RDF is a relational semantics. The model is arrows between things. That
the serialisations don't allow literals in predicate position is a syntactic
restriction, not a semantic one: because semantically one just cannot
impose such a restriction. It is very clear that there are relations between numbers for example.


> 
> On a good day, we can believe what an RDF doc tells us. It does so in
> terms of objects/things and their properties and relationships (o-r-o
> i guess). On another day, we have larger collections of RDF to curate,
> and need to keep track more carefully of who is claiming what about
> these object properties; that's the provenance and quads perspective,
> s-p-o.

As mentioned above o-r-o or s-p-o way of thinking of relations are in my
view ways of thinking of exactly the same thing: arrows between things, or 
relations. This has no bearing on the quads or triple perspective.


> Note that the subject/predicate/object terminology comes from
> the old M&S spec which introduced reification in a ham-fisted attempt
> to handle some of this trust-ish stuff, and that most simple data'
> -oriented stuff uses SPARQL, the only W3C formal spec that covers
> quads rather than triples. So I don't think the community splits
> neatly into two on this, and that's probably for the best!
> 
> RDF processing, specs and tooling are about being able to jump in a
> fluid and natural way between these two views of data; dipping down
> into the 'view from one graph', or zooming out to see the bigger
> picture of who says what.

These are one and the same view. It is just a question of which
world you think is the actual one: ie a question of indexicality. Which 
world am I in.

> Neither is correct, and it is natural for
> the terminology to change to capture the shifting emphasis. But until
> we make this landscape clearer, people will be confused -- when is it
> an attribute or property, and when is it a predicate?

Attribute, property, sentence, these are just the slightly different
ways of saying the same thing. If you try to look here for a solution
to the bigger problem you will not find it. The place to look is at the
possible world semantic level. 

Henry

> 
> cheers,
> 
> Dan
> 
> --
> "There are two kinds of people in the world, those who believe there
> are two kinds of people in the world and those who don't." --Benchley
>

Received on Tuesday, 6 July 2010 08:45:11 UTC