W3C home > Mailing lists > Public > www-rdf-logic@w3.org > May 2001

Re: Desirata for Symbols (was Re: What do the ontologists want)

From: pat hayes <phayes@ai.uwf.edu>
Date: Sat, 19 May 2001 22:01:40 -0500
Message-Id: <v04210143b72c957039bd@[]>
To: Sandro Hawke <sandro@w3.org>
Cc: www-rdf-logic@w3.org
> >        . With my implementers hat, a resource is synonymous with a
> > URI. In code I'm going to call my resource object a Resource, not,
> > SomethingIdentifiedByAURIWhichMayOptionallyHaveAnchorIDs. So when I
> > instruct a machine to hang a property value off a resource, I intend
> > that this instruction will describe the resource not the URI that
> > denotes it. Thus:
> >
> > urn:elvis urn:says urn:thankyuhveriimuj
> >
> > describes nothing about the URI urn:elvis, it's intended to describe
> > whatever urn:elvis denotes: in this case, my neighbours lawn mower.
> > This touches on the matter of social contract Dan Brickley mentioned.
> > We agree that URIs identify things and we agree to call these things
> > resources. If we didn't:
> >
> > urn:elvis, urn:says, urn:thankyuhveriimuj
> >
> > is not any more useful than saying either:
> >
> > "elvis", "says", "thankyuhveriimuj"
> > In RDF, a resource is something identified by a URI (that may have
> > anchor ids) as per rfc2396. That's all there is to it. I find it's
> > useful way to think when it comes to implementing code.  That may
> > seem a backways determination; if I create a URI do I create a
> > resource for it to identify? This is moot, the RDF machine can't
> > access a resource directly anyway, but it allows for the description
> > of say, unicorns.
>What possible advantage does "urn:elvis" (or any other URI-like thing)
>have over "elvis" as a logic symbol?
>1.  We can prevent unintentional re-use.   This is like
>    com.sun.SomeJavaClass or w3c_some_C_library_function.  Doing this
>    allows us to skip a symbol translation stage in reasoning about
>    two different expressions.

Several problems with this include the fact that often, with names, 
one NEEDS to have 're-use' in order to refer to something. That is 
largely what names are for in social use of language, if you think 
about it. But I have argued this to death in earlier threads.

>    I think there are cases, with agents communicating in a multi-path
>    network, where the translation problem becomes impossible to solve
>    without at least a mechanism for generating unique agent (or
>    document) identifiers.  And if you need that generation mechanism
>    for agents, you might as well make it available for all objects.

Not all names are identifiers!  Most objects do not have identifiers 
in this sense.
A name-clash of identifiers is a computational error. Re-use of names is not.

>2.  There are some social mechanisms in place to designate who has
>    authority to define the denotation of the symbol.  The clearest is
>    probably urn:oid, which involves a whole mechanism in
>    international law deligating denotational authority.  (I don't
>    know how well it works, but I've heard it tries.)

Denotational authority? Wow. You and I definitely live in different 
universes. There are no laws about denotational authority. The only 
person who has "denotational authority" (impossible to type this 
without smiling) over the words I use is me.

>    I have no idea how this actually helps, beyond the functionality
>    in point #1.  Who cares if symbols starting urn:oid:1.2.840.113556
>    may only legally be "defined" by Microsoft?  How do we use that
>    fact?
>3.  Some URIs can point humans and/or machines to some definitional
>    text, possibly even some permanent definitional text.  But is
>    there an advantage to
>        "elvis according to the formal definition at http://example.com/elvis"
>        (aka "http://example.com/elvis#elvis")
>    over
>        "elvis234234"        [elvis with some uniqueness mechanism]
>       with the nearby assertion
>        ("elvis234234", formal_definition_website, "http://example.com/elvis")
>    The later form gives us much more flexibilty to explore approaches
>    to "definition", whatever that means.

The denotation of my name is me, not a definitional text.

>4.  Some URIs already have a pretty widely known denotation.  Or do
>    they?  What exactly does "http://www.yahoo.com" denote?  Is it a
>    document, a service, a company, something you type into your
>    browser, or what?  Heck, it's not even a decent URI -- it's
>    supposed to have a "/" on the end.  You can quote RFCs 2396 and
>    2616 at me, but if that meaning isnt exactly matched in the minds
>    of some important group of people (and I would argue it is not
>    yet), does it really matter?

Very good questions.

Pat Hayes

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Received on Saturday, 19 May 2001 23:01:36 UTC

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