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: Mon, 23 Jul 2001 19:26:53 -0700
Message-Id: <v04210114b78289b99f9c@[130.107.66.237]>
To: Brian McBride <bwm@hplb.hpl.hp.com>
Cc: w3c-rdfcore-wg@w3.org
>Aaron,
>
>The thing to bear in mind about this submission is that these
>were not my words.  They were the words (with some HP specific
>stuff removed) of my colleagues who are using RDF in the manner
>described.  This input is from real developers.
>
>Aaron Swartz wrote:
> >
> > On Monday, July 16, 2001, at 02:23  PM, Brian McBride wrote:
> >
> > > (1) In the seller advert it would appear that the seller is
> > > only advertising a
> > > single specific (but under-specified) service, #anon12345 or
> > > whatever, which
> > > would be hard to distinguish from an actual service instance
> > > like #service42.
> >
> > Why would you want to distinguish between the two?
>
>I think the idea here is that there will be URI's
>denoting specific services.  My colleagues are
>interpretting a node with a URI to be denoting
>such a service.  It would be wrong to match a different
>service.
>
>When an anonymous node is specified, then no such constraint
>exists.  Thus a processor would process these two instances
>differently.
>
> > And I see
> > nothing about a URI that licenses you to assume that there is
> > only such thing.
>
>Oh we really do need this model theory don't we.  I tend to think
>of a URI as identifying one thing, and one thing only, but that way
>lies a philosphical debate on the nature of 'one'.  Shudder!

Just sit down and take a few deep breaths.

In a given interpretation it denotes one thing. But then you have to 
ask, what does the reader know about the interpretation the writer 
had in mind when they wrote the RDF? Answer: only what is said in the 
RDF or specified in the semantic rules for RDF. You get the same 
answer if the writer uses an anonymous node or if the writer uses a 
non-anonymous node *which the reader doesnt know anything else about* 
(a skolem name, eg). Either way, all the reader knows is that the 
writer had in mind an interpretation in which some thing exists which 
satisfies whatever they wrote about the thing indicated by the URI.

> >
> > > (2) Similarly in the buyer advert instead of describing a
> > > template, giving the
> > > service a URI would make it appear that I am looking for a
> > > specific service with
> > > that URI.
> >
> > Umm, aren't you? What's the difference? In both you're looking
> > for something with these properties.
>
>The difference is that when a URI is specified the assumption is
>that someone, somewhere has defined a 'well known' name for this
>service.

NO!!  That is NOT a valid assumption. URIs need not be 'public' 
names, in the sense that they are shared between more than one user. 
I can invent brand-new URIs and use them , and you might have no idea 
what I am talking about.

>The essence of this issue seems to involve the idea that the
>act of naming something in the internet is somehow, special.

I don't think the internet makes any difference. If I use a name in a 
private way, putting it on the internet doesn't make it any more 
obvious to you what I mean. The internet is only a file interchange 
protocol, when one comes right down to it; it doesn't work semantic 
miracles or make people telepathic.

>That if a processor is told that something has URI ISBN-12345
>or whatever, it had better not match that with anything that
>it does not 'know' is named ISBN-12345.  On the other hand,
>if a node is not named, then it can be matched with anything
>that matches its properties.

I dont think this is in any way valid or warranted. It amounts to a 
global unique-name assumption, which is obviously not correct on the 
Web, since it isnt even correct on many web pages. It may be correct 
(in an ideal world) for URL's, but it cannot be assumed for all URIs

>I'm not sure that standard FOL captures this.  FOL is built
>around a conceptual model where there can be many interpretations
>for statements in the FOL.

Almost all languages are bult around that idea.

>But that is not the situation we
>are in here.  We have one interpretation - its a mapping to
>the world out there.  Intuitively I feel that makes a difference.
>That makes naming special.

I couldn't disagree more. We do NOT have one interpretation. All we 
send one another are assertions, not interpretations, and if the 
sender wants to constrain the receiver's interpretations then he 
needs to send enough content to make the constraint explicit. I might 
have one interpretation in mind, but there is no way for you to know 
what it is; unless of course I only use literals to say what I mean.

Pat Hayes

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Received on Monday, 23 July 2001 22:26:47 EDT

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