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homonym URIs (Re: What if an URI also is a URL)

From: Sandro Hawke <sandro@w3.org>
Date: Mon, 11 Jun 2007 18:11:26 -0400
To: Pat Hayes <phayes@ihmc.us>
Cc: semantic-web@w3.org
Message-ID: <27121.1181599886@ubuhebe>


Pat Hayes <phayes@ihmc.us> writes:
> Tim, as this discussion gets to the heart of what
> Ive been trying to argue for several years,
> please take the comments below as intended in a
> spirit of analysis rather than just pins and
> angels.

Pat, I'm going to jump in here, if you don't mind.  I think my position
on these issues is pretty much the same as Tim's but I could be wrong.
I don't argue that John's "dance" isn't required, just that part of the
Semantic Web version of the dance is: don't make your URIs unnecessarily
ambiguous.  One might even say: don't pun.

> And what about a URI
> that I own and wish it to denote, say, the planet
> Venus, or my pet cat? What do I do, to attach the
> URI to my intended referent for it?

You publish a document (an ontology) so it's available through that URI.
If it's a hash URI, you publish the ontology at the non-hash version.
If it's a slash URI, you publish the ontology at the far end of a 303
redirect.  And you content-negotiate HTML and RDF.

So when users paste that URI into their browser, they get the official
documentation about it.

And when RDF software dereferences that URI, it gets some logical
formulas which should be understood (like the HTML) to be asserted by the
URI's owner/host/publisher.  Those formulas constrain the possible
meanings of that URI, relative to other URIs.  They can't nail a URI to
Venus, but they can use other ontologies to provide useful (and possibly
very constraining) information, like that it's an astronomical body with
a mass of about 5e+24kg.

My advice here is, I confess, not widely followed.  But I hear more and
more people converging on the idea that this is both practical and
likely to be sufficiently effective.

> The point surely is that URIs used to refer (not
> as in HTTP, but as in OWL) do *not* have a
> standardized meaning. Standards are certainly a
> chore to create, but they only go so far. OWL
> defines the meanings of the OWL namespace, but it
> does not define the meanings of the FOAF
> vocabulary,

No, that's up to the owner(s) of the FOAF terms.

> or the URIrefs used in, say,
> ontologies published by the NIH or by JPL.

And that's up to the NIH and JPL, respectively.

> The
> only way those meanings can be specified is by
> writing ontologies: and finite ontologies do not
> - cannot possibly - nail down referents
> *uniquely*. 

Ah -- there we go.  There must be a long history of this subject in
philosophy.  Can things ever be nailed down uniquely?  I haven't a clue.
But that's the wrong question.  In this thread, I don't think we're
talking about whether we can really be sure what we mean when we say
such a URI denotes Venus.  Instead, we're talking about whether it's a
good practice to use a single URI to denote clearly distinct things,
such as:
   (1) the second rock from the sun
   (2) the Roman goddess of love
   (3) a star tennis player
   (4) ... etc
The term "ambiguity" covers both these issues, but we don't need to
combine them.   The first is a kind of imprecision, a fuzziness, while
the second is the re-use of a word for a second meaning, a homonym.
(Homonyms seem to be called "overloading" in computer programming.)

I think we know how to work with homonyms, but since we're engineering a
new system, it seems like a good design decision to forbid them, doesn't
it?

    -- Sandro
Received on Monday, 11 June 2007 22:11:31 UTC

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