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Re: Three solution designs to the first three Graphs use cases

From: David Wood <david@3roundstones.com>
Date: Tue, 31 Jan 2012 17:47:54 -0500
Cc: Andy Seaborne <andy.seaborne@epimorphics.com>, "public-rdf-wg@w3.org WG" <public-rdf-wg@w3.org>, Sandro Hawke <sandro@w3.org>
Message-Id: <38D065CF-BC2E-4E9A-B92B-7BEC2DB7298F@3roundstones.com>
To: Pat Hayes <phayes@ihmc.us>
Hi all,

On Jan 29, 2012, at 14:34, Pat Hayes wrote:
> On Jan 27, 2012, at 1:13 AM, Andy Seaborne wrote:
>> On 27/01/12 03:45, Sandro Hawke wrote:
>>> On Thu, 2012-01-05 at 11:09 +0000, Andy Seaborne wrote:
>>>> - - - - - - - - - -
>>>> 
>>>> I find the name TriG/REST confusing because, for me, identifying the
>>>> dereference action is modelling REST which is the other
>>>> 
>>>> It's more like "TriG/WebCache" -- only one instance of the graph
>>>> containers state is possible.
>>> 
>>> I don't follow your logic.   My thinking in picking the name "TriG/REST"
>>> is that the implied relation is the relation that's kind of at the core
>>> of REST, the relationship between a thing and its 'state'.
>> 
>> The difference is time.
>> 
>> The relationship of URI to value is time-varying in REST.  RDF does not have that natively so using events (or etc) is a way of having a world model with fixed facts that included time-based actions.
>> 
>>>>> g log:semantics { s p o }.       # TriG "REST" semantics
>> 
>> But that only works for a single point in time - a single run and observation in cwm.  Indeed, rerun the rules and you may well get a different answer (c.f. tax returns).
>> 
>> You can't record that as a fact for a time-varying graph container.  You need an indirection though the act of reading the value.
>> 
>> Test case - how to say :g was { :s :p :o } at time T1 and { :s :p :z } at time T2.
> 
> Right, exactly. This is THE semantic issue here. If we are planning to incorporate any kind of state- or time-sensitive meanings into the RDF semantics, then the whole RDF model needs to be re-thought from the ground up. RIght now, RDF HAS NO NOTION OF STATE OR TIME OR CHANGE IN IT ANYWHERE. (Sorry about the shouting, but it is apparently needed.)  If we are going to put that idea in, the change to RDF will be far more profound and far-reaching than anything we have considered so far. The resulting language will not resemble current RDF at all at the semantic level. It will no longer mesh with OWL or RIF or any of the other formalisms that have been built on it.  Is this kind of a change within our charter?


No, we are not chartered for that, but do we (want | need) to be?

Does the RDF data model need to understand the meaning of the predicate "at time x"?  I don't think so.  We as humans understand the concept of time, but RDF doesn't and probably shouldn't.  If RDF doesn't understand the "at time" predicate in any special way, don't we duck this entire issue?

To me, this is a similar argument to the one about OWL inferencing; meaning is brought in above the RDF level.

Regards,
Dave


> 
> Pat
> 
> 
> 
>> 
>> 	Andy
>> 
>> 
> 
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Received on Tuesday, 31 January 2012 22:48:23 GMT

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