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

From: Brian McBride <bwm@hplb.hpl.hp.com>
Date: Thu, 19 Jul 2001 10:54:08 +0100
Message-ID: <3B56AE40.D39077C2@hplb.hpl.hp.com>
To: Frank Manola <fmanola@mitre.org>
CC: rdf core <w3c-rdfcore-wg@w3.org>
Hi Frank,

Frank Manola wrote:
> 
> Brian--
> 
> I wonder if you could resend your example, annotating it with which
> things are supposed to be the anonymous resources, and which aren't?  I
> frankly (how else can I talk?) found it difficult to properly interpret
> it.  Some of the comments below may be based on the resulting
> misinterpretation.

Good point.  This is how the use case came to me and I just passed it
straight on.  I should have included a translation.  Here is one now:

#advert123 :role "buyer"; 
           :description [:product :roses; 
                         :quantity [:units :kg; :minValue "100"]].

translates to:

<#advert123> <foo:role>        "buyer" .
<#advert123> <foo:description> _:service .
_:service    <foo:product>     <foo:roses> .
_:service    <foo:quantity>    _:q .
_:q          <foo:units>       <foo:kg> .
_:q          <foo:minValue>    "100" .

i.e this is advert placed by a purchaser who wishes to buy roses in
minimum quantities of 100.

and

#advert456 :role "seller"; 
           :description [:product :roses; 
                         :quantity [:units :kg; :maxValue "500"]].

translates to:

<#advert456> <foo:role>        "seller" .
<#advert123> <foo:description> _:service .
_:service    <foo:produce>     <foo:roses> .
_:service    <foo:quantity>    _:q .
_:q          <foo:units>       <foo:kg> .
_:q          <foo:maxValue>    "500" .

i.e. this is an advert placed by a seller who can sell roses in
quantities upto 500.

I've checked with my source and this is the correct.


> 
> For example, there seems to be this assumption that an anonymous
> resource represents a variable in a query or template that is to be
> bound to specific instances (e.g., in the book seller example).

Err, I'm not sure why this is being raised in the context of this use
case.  I see no queries in this use case.  I see only assertions
about advertisments.

> However, I don't think this is the proper interpretation of any of the
> uses of anonymous resources in the M&S, the first one being "The
> individual whose name is Ora Lassila, email <lassila@w3.org>, is the
> creator of http://www.w3.org/Home/Lassila."  Rather, I think the basic
> interpretation of RDF statements is that of being assertions, and in
> some cases you wind up asserting the existence of something that you
> don't have a URI for, so you generate an identifier for it (e.g., the
> "individual" in the previous statement).  I amplified on this in one of
> my earlier messages [and I'm using the present message as a stake in the
> ground;  I'm composing a longer dissertation on this that I'll send
> later, since I have an action item on anonymous resources].

That seems plausible to me.

> 
> Your comment above about a URI only representing one thing suggests
> looking at the problem from the opposite direction too.  That is, while
> sometimes you may want to use an anonymous resource to refer to a "real
> thing" (like the "individual" whose name is Ora Lassila), in other cases
> you may want to use a genuine URI to refer to a template, or one of its
> parameters.  These are, after all, real things that you want to be able
> to talk about (particularly in the context of Web applications).  The
> fact is that there isn't really any built-in interpretation (at least
> not that I can see) that URIs only identify things that "really exist"

I'm not sure how to decide what really exists and what doesn't - I hope
we can stay away from that question.  I personally would be happy to have
a URI to denote a unicorn in some fairy story.

> (in some sense) and anonymous resources only identify variables to be
> matched.  Rather, these are interpretations we assign to them in
> specific uses.  I can easily imagine a "template" (e.g., a specific
> purchase order form) having a URI, with each of its component items also
> having a URI (I might want to describe its format and semantics, for
> example).  A specific instance of that form, partially or totally filled
> in with specific values, might have a separate URI.  There would
> probably be machinery for relating the template to the filled in
> instance, but it would be part of some application semantics, not
> necessarily built into the semantics of RDF.

I'm not following the point you are trying to make here, but the
thought in my head is that we need to take care to distinguish
between the name of a 'variable' and the name of the thing
the variable is bound to.

[...]
> > 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.  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'm not sure what you mean here.  

Neither am I :(  I said to express and intution that isn't well formed
in the hope that someone might shed some light.

> If you mean that FOL statements can
> refer to both real things and "conceptual" things like templates or
> queries, that's true (e.g., I can describe the contents of a query in
> FOL), but, as I tried to argue above, so can URIs.  What seems to be
> happening in these examples, though, is that we're taking some syntax,
> and interpreting it in slightly different ways depending on whether we
> think we're talking about a query, or about a set of assertions.

I see no queries in the use case - only assertions.

What I'm getting at that traditional logic is about designing formal
systems that are true under any interpretation.  That's not what we
are dealing with here.

>  I
> discussed this in
> http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Jun/0559.html
> I think we need to be very careful about this.
> 
> This isn't to say that there might not be a place for variables in RDF.
>   I just don't think that that's automatically the appropriate
> interpretation of anonymous resources.
> 

Brian
Received on Thursday, 19 July 2001 05:56:44 EDT

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