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

Re: A use case for anon nodes - action from telecon

From: pat hayes <phayes@ai.uwf.edu>
Date: Thu, 26 Jul 2001 14:32:25 -0700
Message-Id: <v0421010fb7863ac11bba@[130.107.66.237]>
To: Graham Klyne <Graham.Klyne@Baltimore.com>
Cc: w3c-rdfcore-wg@w3.org
>At 12:19 PM 7/26/01 -0700, pat hayes wrote:
>>I think this example has been valuable because it illustrates a 
>>much bigger and more important point than the one we started with. 
>>The implied meaning to an English speaker is *completely 
>>irrelevant* here. RDF is supposed to be used by software agents, 
>>not English speakers (if we could rely on the native savvy of 
>>English speakers, we could do it all in HTML). So the only content 
>>that any piece of RDF (or DAML, or KIF, or any of these 'formal' 
>>languages for capturing content) actually contains is what some 
>>mechanical agent could infer from it (together with whatever other 
>>pieces of RDF it is able to glean from various sources, of course.)
>>
>>If you apply that criterion to Brian's example, and if you take it 
>>to be an assertion, then all that you could possibly infer is that 
>>four things exist and a few relations are true between them. If 
>>this is supposed to convey the fact that one of these things is a 
>>'service' and therefore that it implies that a lot of other things 
>>exist (eg batches of roses which are available for sale or purchase 
>>-I've lost track of whether we are selling them or buying them), 
>>then something needs to say that.  Nothing in Brian's example seems 
>>to say that, however, so there is no basis for anything to be able 
>>to conclude it. (I would hazard a guess that the only way to say 
>>what needs to be said here is to use a universal quantifier, by the 
>>way.)
>
>Yes... I think that the examples were incomplete in that a 
>definition of specific symbols used (to be guessed at from the names 
>used) was needed.  Without this, there was no logical distinction 
>between the buyer and seller examples (modulo a small change of 
>quantity values).
>
>But, at some point, a computer program has to interface with the 
>real world.  Maybe the only difference between the buyer and seller 
>processes is that the results of invocation of the service are 
>delivered to different printers.  It may happen that one printer is 
>in a warehouse with a staff that reads the requested quantities and 
>other details, picks the desired roses off the shelf and puts them 
>in a van for delivery to the stated address.  That would be the 
>seller service.  Another printer might be serviced by a staff who 
>pick up the details and send their van to a designated address to 
>collect some roses.  That might be the buyer service.
>
>How much of this external-world difference do we need to encode in 
>the computer program?  It may be that the only difference between 
>the buyer and seller, as far as the program is concerned, is an 
>associated port address that selects an appropriate printer to 
>receive the service instruction.  So if the previous examples were 
>augmented with something like:
>
>   buyer usesPrinterPort "1" .
>
>   seller usesPrinterPort "2" .
>
>that states a logical difference between the services.

Well, no. Of course programs rely on such things all the time, but my 
point is that in cases like this the information is NOT being 
conveyed as a 'logical difference', ie in this context, in the RDF, 
but in some other way that is invisible to an RDF processor. Which is 
fine, as long as we face up to that. In the meantime, however, I am 
assuming that what we are supposed to be focussing on here is what 
can be said in RDF.

>But the context within which the services are deployed (defining an 
>interpretation?) is part of the situation in which we care about the 
>results of the computation.

If we were programming local computations in a limited, known 
context, then we could rely on all kinds of assumptions. But RDF is 
supposed to be publishable on the Web, right? What 'context' can be 
assumed between a publisher of a web page and a reader of that web 
page, beyond the protocols used to transfer the information?

>Maybe this goes against normal practice for model theory.  I notice 
>that you said in your strawdog note that common model theory 
>practice is to make the available domain of interpretation as 
>general as possible.  I suppose that the vital thing we need is for 
>programs to exchange information that is  constructed using the same 
>assumptions about the interpretation.

If there are any global assumptions then by all means let us build 
them in. In the strawdog, for example, I assume that literals have a 
fixed global interpretation which never varies, so anyone using a 
literal can assume that any reader will have the same interpretation. 
We can have fixed interpretations for things like rdf:subject (in 
fact for anything starting rdf: or rdfs:). But how do we establish 
globally fixed meanings for things like wholesaleSupplierOfRoses ?

> The fewer such assumptions, the less room there is for a 
>communication to be misinterpreted.  But I'm pushed to see how we 
>can make a useful program without many assumptions about the 
>environment it communicates with.

I thought that was the central point of RDF. It certainly is for DAML+OIL.

Pat

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Received on Thursday, 26 July 2001 17:32:16 EDT

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