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Re: Web Semantics of Datasets (v0.2)

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 12 Oct 2011 00:52:52 -0500
Cc: public-rdf-wg <public-rdf-wg@w3.org>
Message-Id: <B43062E2-89F1-486E-8E30-B5BB51E38E5C@ihmc.us>
To: Sandro Hawke <sandro@w3.org>
On Oct 10, 2011, at 8:54 PM, Sandro Hawke wrote:

> On Mon, 2011-10-10 at 15:19 -0500, Pat Hayes wrote:
>> On Oct 10, 2011, at 6:30 AM, Sandro Hawke wrote:
>>> Here's some revised wording for the proposal, getting a bit closer to
>>> spec text.   It's still somewhat informal, and mixing normative and
>>> non-normative bits, and best-practice.   And it's not as clear as it
>>> should be about handling change over time.
>>>   -- Sandro
>>> ===
>>> A dataset D is true
>> You have to say, true in an interpretation, and modify the rest of the phrases accordingly.
>>> iff (1) its default graph is true and (2) for
>>> every pair of <N,G> in D, N names something (a "resource", sometimes
>>> called a "g-box") which, at every time T in R, has G as its current
>>> state.
>> What is R? 
> R is a set of points in time, as discussed elsewhere.   To me that seems
> like a perfectly reasonable way to think about this

Can you say what you think a "point in time" is? 

> , but *shrug* feel
> free to come up with some other way to keep graphs in sync.  (see
> example at the end of this email.)
>>> It follows from AWWW that if N is an IRI which can be dereferenced,
>>> a successful, correct dereference of N at any time T in R must yield
>>> a serialization ("representation") of G.
>> No, that does not follow. There is no immediate connection between being a name of something and dereferencing to something. If we want this relationship, we have to state it explicitly. Also, you have stated this using a modality ("can be") which opens up a huge can of worms. (What if it could be dereferenced but never, in fact, was? Did it name the graph under those circumstances?) I would strongly suggest that we avoid this kind of language.
> The heart of ReST and AWWW is that dereferencing an IRI yields a
> representation (serialization) of the state of the thing named by that
> IRI.  

No, of the thing "identified" by that IRI. This notion of identification is different from, and need have nothing to do with, the notion of naming. If we want them to be the same (sometimes, under some conditions) then we have to say that explicitly, in the semantics. 

>  That's the "immediate connection" I'm using.  So, doesn't it
> follow from that?

No, because that usage of the word "representation" is idiosyncratic and, on the face of it, unrelated to the broader semantic notions. Im not saying that they cannot be related (they can), but they are distinct, and unless something is said which relates them, they are not related and have nothing particularly to do with one another. The current RDF semantics states explicitly that the semantic interpretation of a URIref need not be related to what HTTP (or any other XXTP) does with the URI. We could change this so that the RDF semantics embodies the http-range-14 decision, for example. Is that widely accepted by the WG? 

> I'm not asking for anything different in the RDF semantics than is in
> there now with the way I can currently say in RDF:
>  <http://www.w3.org/People/Berners-Lee/card> foaf:age 56.
> That works fine in the RDF semantics today, doesn't it?   

Yes, if it is asserted timelessly, with no notion of "now" involved. If you want this to change from true to false on TIm's next birthday, then no, it does not work that way in the current RDF semantics. There is no notion of truth-relative-to-a-time-interval in the current semantics. Putting that into RDF would make it into something like a context or hybrid logic. For a discussion of the problems in doing this in a web-based logic, see http://www.ihmc.us/users/phayes/IKL/GUIDE/GUIDE.html 
and especially the section on contexts and modalities. 

> All I'm asking
> for is a bit more understand of how it works, and some vocabulary for
> machines to share the metadata they need to keep things straight when
> they fetch that kind of thing from different places at different times.

That "all" you are asking for is a research project in temporal logic. I am not going to do this project. If someone else in the WG (you?) wants to tackle it, I'm happy to wait until they get it sorted out. 

> (And then I also want to apply it to dereferencing.)

First you have to get the research done, then maybe you can apply the results. Good luck. 


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Received on Wednesday, 12 October 2011 05:53:33 UTC

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