W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > September 2001

Re: Working on glossary

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Wed, 12 Sep 2001 12:16:26 +0100
Message-Id: <5.1.0.14.2.20010912114845.03ac3a80@joy.songbird.com>
To: pat hayes <phayes@ai.uwf.edu>
Cc: w3c-rdfcore-wg@w3.org
At 08:16 PM 9/11/01 -0500, pat hayes wrote:
>>Yes... I'd have thought the things that are "on the web" (resources with 
>>retrievable entities) are similarly limited when compared with the world 
>>of experience available to and described by us humans.
>
>We are getting our languages crossed here. I have been excorciated by W3C 
>folk in the past for claiming that only documents are 'on the web', and 
>told that this phrase is intended to mean not that something is 
>*retrievable* through the Web, but that it can be *mentioned* on the Web. 
>So for example, the existence of a URI convention for telephone numbers 
>means that every telephone is "on the web". So in this sense of "on the 
>web", the entire sum of all past and future human experience is indeed on 
>the web. Nothing to do with mere retrieval.

I accept I'm probably abusing the adopted terminology there.  My real 
thrust here was to get the ideas straight for things which do have 
retrievable entities, before trying to tackle the potentially trickier 
problem of non-retrievable entities.  A kind of walk-before-run strategy.

[...]

>>In addition to the octet-sequences that are web-retrievable entities, I'm 
>>suggesting that the real world objects are (also) part of the resource 
>>extension I mentioned previously, rather than the resource directly.
>
>That would be one way to go. It would complicate both RDF and its 
>semantics, though. Presumably for example it would not be correct to 
>interpret <s p o> as meaning that a relation holds between s and o, since 
>sometimes it would mean that the relation held between the 'extension' of 
>one or both of s and o.

I don't follow that.  If I understand correctly, if <s p o> is asserted all 
the model theory tells us is that <s o> is in the relational extension of 
p.  That seems to stand independently of whether or not s and o have what I 
called "resource extensions".  What it means for <s o> to be in IEXT(p) 
seems to be a matter for the particular interpretation chosen, which is not 
specified by the MT.

Oh, hang on, s p and o *are* interpretations, aren't they?  ... [continued 
below]

>... In fact this is what I thought would be necessary when I first agred 
>to try to do a model theory, and I was considerably relieved to find that 
>it apparently wasn't necessary. (It can get awfully complicated. Suppose 
>one URI denotes a document which contains another URI, for example; do we 
>have to say that the chain of retrievals keeps going until it terminates 
>in something with an extension? (Is there any guarantee of termination? 
>What about reference loops?) If we don't, what sense can we make of the 
>triple?)
>
>>
>>>>Then, the resource can correspond to the current weather forecast, but 
>>>>its extension includes the set of all weather forecasts for all 
>>>>times;  the particular member of that extension one retrieves depends 
>>>>on when the retrieval is performed.
>>>
>>>We could do something like this, but this is what I meant by a modal 
>>>(possible-world) semantics, since the denotation here ought to be not 
>>>the entire extension (in your extended sense) but the particular member 
>>>of it at the time the query was made. The semantics on this case would 
>>>need to introduce a notion of times and time-relations in order to make 
>>>snes eof this notion of 'now'. (It could be a very simple notion, eg 
>>>points with a total order, but the point is that we would need to say 
>>>*something* about it.)
>>
>>Yes, indeed, but such (time-sensitive) semantics would be part of the 
>>semantics of a resource, about which the RDF model theory you have 
>>described seems to be agnostic.
>
>My one is, yes. But I thought you wanted it to not be.

I was about to say "no, see above".  But realized that I was trying to talk 
about an interpretation of an interpretation which isn't a defined 
concept.  So I'll regroup:

I wasn't expecting time dependence to be reflected directly in the MT, but 
introduced somehow through the interpretation or URIs.  The MT tells us:

(a)  the interpretation of a URI is something called a "resource"

I am suggesting an addition:

(b)  a "resource" is some abstract thing, having an extension (possibly 
empty, possibly infinite) that is a set of entities.  These entities may be 
web-retrievable octet sequences.   And when we're ready to try running, 
they might be physical objects.

This would act as a constraint on any interpretation that satisfies the 
MT.  But the exact relationship between the resource and its entities is 
not specified by the model theory, and I don't see that it needs to be.  In 
some cases, the members of the extension may be time-specific.

It feels that what I am suggesting here is like a level of indirection 
through the thing we call a "resource".  (There's a saying that there's no 
problem in software engineering but can be solved by an additional level of 
indirection.  Maybe there's a KR equivalent:  no problem not solved by an 
additional level of extension? :-)

#g


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Graham Klyne                    MIMEsweeper Group
Strategic Research              <http://www.mimesweeper.com>
<Graham.Klyne@MIMEsweeper.com>
------------------------------------------------------------
Received on Wednesday, 12 September 2001 07:48:39 EDT

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