W3C home > Mailing lists > Public > semantic-web@w3.org > June 2007

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

From: Richard Cyganiak <richard@cyganiak.de>
Date: Tue, 12 Jun 2007 09:32:06 +0200
Message-Id: <D1835087-5AF5-434B-9BBD-7135B93129D1@cyganiak.de>
Cc: Sandro Hawke <sandro@w3.org>, Pat Hayes <phayes@ihmc.us>, semantic-web@w3.org
To: Rikkert Koppes <rikkert@finalist.com>

Keep in mind that an OpenID, in web architecture terms, is an  
information resource. A document. It's your passport, not you. Same  
for an OpenID alias. Thus, using your homepage as an OpenID alias  
simply makes your homepage a multi-function document. This doesn't  
make its URI a homonym. “Swiss army knife” isn't one either.

See also Tim's response to DavidP earlier in the thread.


On 12 Jun 2007, at 06:59, Rikkert Koppes wrote:

> Sure, forbidding homonyms seems like a gooed idea, but I wonder if  
> this is also possible. Doesn't homonym URI alread exist?
> To illistrate an example: www.example.com might be (identified as)  
> a person's home page. But it might include a link element linking  
> to an openId endpoint (www.example.com/openId, say). We do have two  
> different URI's for two different things, but www.example.com is  
> also a alias for the openId endpoint (by virtue of the link element).
> What should we do when making statements about someone owning the  
> site and also using the openId alias? Can we safely say that the  
> thing the uri identifies (the web site, document) is in fact the  
> openId alias? I don't think so. It is the uri itself, so we  
> therefore might contain it as a string literal in a statement about  
> the person's openId alias.
> Rikkert Koppes (mophor)
> Sandro Hawke schreef:
>> 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 Tuesday, 12 June 2007 07:33:00 UTC

This archive was generated by hypermail 2.4.0 : Tuesday, 5 July 2022 08:45:01 UTC