W3C home > Mailing lists > Public > www-rdf-interest@w3.org > May 2004

RE: URIs may not mean *exactly* what you think

From: John Black <JohnBlack@deltek.com>
Date: Thu, 6 May 2004 13:31:38 -0400
Message-ID: <D3C8F903E7CC024C9DA6D900A60725D905393889@DLTKVMX1.ads.deltek.com>
To: "Benja Fallenstein" <b.fallenstein@gmx.de>, "Rhoads, Stephen" <SRhoads@ThruPoint.net>
Cc: <www-rdf-interest@w3.org>

> From: Benja Fallenstein
> Sent: Tuesday, May 04, 2004 3:19 PM
> Hash: SHA1
> Rhoads, Stephen wrote:
> | <slightlyOffTopic>
> |
> |>>I understand what you mean: intuitively, "the" right
> |>>range of pet:owner might be foaf:Person.
> |
> | Until someone comes along and wants to say:
> |
> | Benji rdf:type ex:Dog
> | Benji pet:owner ex:AtlantaPoliceDepartment
> I was assuming that pet:owner is defined so that it does have 
> rdfs:range
> foaf:Person, in a similar way that foaf:mbox is defined to be 
> an inverse
> functional property.
> (I'm aware that pets may be 'owned' by something else than a person,
> although I was more thinking of e.g. families. Restricting 
> pet:owner to
> people makes sense when you're specifically interested in 
> pets owned by
> individual persons.)
> What I think you're ignoring above is that text in URIs and the qnames
> that abbreviate them is only mnemonic -- it does not *define* what the
> URI means, it's only a hint.
> I think that's an important point. You say,
> | What to do?  Range is something broad like "Entity"?  And 
> when someone
> finds
> | a valid use for pet:owner with a "non-Entity"?
> but if the precise meaning of pet:owner does *not* include general
> "entities," much less "non-entities," such a use would not be 'valid'
> and would not make sense. If I see a use for
> ~    Annie foaf:mbox <mailto:AandEMiller@example.com>
> ~    Elin  foaf:mbox <mailto:AandEMiller@example.com>
> then that doesn't change the fact that it's not a *valid* use -- even
> though the address was obviously specifically created to be used by
> Annie and Elin together, so if you look only at the qname, 
> 'foaf:mbox,'
> the above makes perfect sense. The problem is that it defies 
> one of the
> very purposes of foaf:mbox, namely identifying people (well, entities
> ;-) ) uniquely.
> If I want to express the above semantics, I should make up my own
> property that is defined with the semantics I intend.
> And the very same thing applies to "global domain and range 
> constraints
> within the context of the Web." Their point is being able to infer
> something -- in our example, that the object of pet:owner is a person.
> There are other uses, too, but this is the most fundamental 
> one. If you
> don't like that from a pet:owner triple you can infer that 
> the object is
> a foaf:Person, you can make up your own property.
> So my point in this e-mail is: You seem to be saying that 
> global domain
> and range constraints should not be used -- or maybe even ignored when
> they are used -- because they prohibit valid uses of certain 
> properties.
> But if the owner of the property gives it a range constraint that says
> that object X is not in its range, than using it with an object X
> *cannot* be a valid use of the property. You could say that 
> prohibiting
> these uses is pointless nitpicking, but it's not, because it is what
> allows us to make useful inferences! And nothing gets less expressive,
> because you can make your own URI that expresses the 
> semantics you want.
> You could say that it's better to use standard terms, but it is NOT
> better to use standard terms for something else than what they were
> defined for -- and that is what you do if you violate the 
> owner's domain
> or range constraints.
> So it's not domain and range constraints that are the problem, it's
> ignoring the URI owner's definition of a term, including those
> constraints, that is the problem. Looking at the name of a property
> doesn't suffice to use it correctly.

It helps me to rephrase all occurrences of the words "meaning" or  
"definition" with a phrase that has slots for the speaker and the 
context, something like this:

 ?speakerAgent meansBy ?term inContext ?namedGraph. [1] or
 ?term meansTo ?listenerAgent inContext ?namedGraph.

Specifying *who* means something by pet:owner in a 
particular *context* removes all sorts of confusion for me. I believe 
the concept of Speaker Meaning, rather than URI Ownership is the 
essential factor here.  And specifying the context allows for a speaker 
to use a term or URI to mean something different in different contexts, 
which is a frequent occurrence.

This also generalizes nicely by allowing ?listenerAgent to take on values 
equal to groups of people. Terms can mean different things to different 
groups of people in different contexts.

If there is any form of global or timeless meaning I think it will have 
to take the form of a catalogue of uses (instances of meanings) of that 
term, such as is done for English in the Oxford English Dictionary Based 
on Historical Principles. http://dictionary.oed.com/about/ 

John Black
[1] http://www.wiwiss.fu-berlin.de/suhl/bizer/SWTSGuide/carroll-iswc2004.pdf.

> (I think that's an important point, which is why I reply so 
> elaborately.
> Sorry for the long mail.)
> Cheers,
> - - Benja
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> Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org
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Received on Thursday, 6 May 2004 13:31:55 UTC

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