RE: URI Declarations [Usage scenarios 4 and 5]

> From: Pat Hayes [mailto:phayes@ihmc.us]
>
> At 12:39 AM +0000 3/3/08, Booth, David (HP Software - Boston) wrote:
> > [ . . . ]
> >SCENARIO 4: Gary publishes a lumber ontology at
> >http://gary.example/lumber.  The ontology includes the concept of a
> >standard 8-foot "2x4", which is denoted by the URI
> >http://gary.example/lumber#2x4x8.  Pat is writing a set of
> >assertions to describe the house he plans to build, and he is
> >interested in Gary's #2x4x8 URI, but during testing he notices that
> >Gary's ontology (erroneously) asserts that "30.49 inches = 1 foot".
> >For perhaps obvious reasons, Pat does NOT wish to accept that
> >assertion.
> >
> >Question: Should Pat use http://gary.example/lumber#2x4x8 to denote
> >a standard 8-foot "2x4" anyway?
> >
> >My answer: No.
>
> OK, we disagree. I think I should contact Gary and point out to him
> his error,

Hmm, you have a good point.  I should have used a little different
example to differentiate between two cases:

4a. The case in which the question of whether the ontology is
wrong is somewhat subjective.  This is the case my answer should
have been addressing, but I didn't describe the use case that way.  Sorry.

4b. The case in which the ontology was correct for a long time,
and became well used in the community, but subsequently became
erroneous -- perhaps due to a clerical error, or maybe because
the domain ownership was lost or hijacked.

I'll try to write these up when I have time.  In the meantime, I'll address your comments below as though they pertained to 4a.  I *do* think the approach you describe would be appropriate for scenario 4b, but I think 4b should be viewed as an unusual circumstance -- far less common than 4a.

> and use his URI when I do so. If I have no way to contact
> him, I should publish an ontology using his URI but correcting his
> error, and maybe (if possible) indicate explicitly that this ontology
> is a correction to his ontology, which is (in my opinion, of course)
> deprecated. Maybe I can include an annotation property to a comment
> indicating the reason (for humans to read). The world now has two
> versions of an ontology, and its up to others which they want to use.

And therein lies the problem with the approach that you're describing.  The world is now faced with the problem of deciding which ontology to use.  Compare this with the architectural approach that I described for URI declarations: One forces the world to decide which *ontology* to use -- I'll call this the ontology redefinition approach -- the other forces the world to decide which *URI* to use.  On the face of it, those options may seem quite equivalent, because they both force a human to make a value judgement that is not likely to be automatable.  But they're not equivalent.

Under the ontology redefinition approach, given a set of assertions, an application cannot determine the meaning of those assertions without *first* involving the human judgement step of searching out the possible ontologies that might be defined for each URI that is used, and deciding which one to invoke.  Under the URI declaration approach, except in case 4b (equivalent to domain hijacking), an application can readily determine the meaning of those assertions.  The human is only forced to search out alternate URIs if he/she does not like a particular URI declaration.

>
> >  Pat should either find a different ontology to use, or mint a new
> >URI and indicate its relationship to Gary's URI.
>
> The relationship would be owl:sameAs, so what's the point of minting
> a new URI? All the semantic consequence, for good or ill, follow in
> the same way.
>
> >For example, Pat could make a copy of Gary's ontology (with Gary's
> >permission, of course), delete the offending assertion, change every
> >occurrence of "http://gary.example/lumber" to
> >"http://pat.example/lumber" and publish the new ontology at
> >http://pat.example/lumber.    The assertions for his house should
> >then use http://pat.example/lumber#2x4x8 instead of
> >http://gary.example/lumber#2x4x8.
>
> WHY should I do this? What is the PURPOSE of this recommendation?
> What utility does it serve?

It conforms to an architectural approach that allows the meaning of Pat's assertions to be readily determined by other applications  -- to the extent that applications can ever determine meaning, that is -- without involving human intervention or judgement (except for case 4b).   That's a big benefit.  It helps the Semantic Web work.

>
> >
> >SCENARIO 5: Helen is writing some assertions about the color of
> >concrete, and is also interested in using a URI from Gary's ontology
> >to denote concrete: http://gary.example/lumber#concrete.  Helen's
> >application makes no use whatsoever of linear dimensions, so
> >although she is aware of the erroneous assertion that Pat
> >discovered, it does not interfere with her application.
> >
> >Question: Should Helen use http://gary.example/lumber#concrete to
> >make assertions about concrete?
> >
> >My answer: She may, but she probably shouldn't, because it would
> >severely restrict the reuse of her assertions.
>
> My answer: The use of a URI does not restrict re-use of assertions
> involving that URI in any way whatsoever. There is no mechanism in
> Web architecture available to enforce such a 'restriction', any more
> than there is to architecturally restrict what use is made of a Web
> page once it is published.

Sorry, I did not mean "restrict" in the sense of "prohibit".  I mean that Helen's use of that URI would severely limit the *usefulness* of her assertions to others (because many applications would need "12 inches = 1 foot" instead of "30.48 inches = 1 foot".


David Booth, Ph.D.
HP Software
+1 617 629 8881 office  |  dbooth@hp.com
http://www.hp.com/go/software

Opinions expressed herein are those of the author and do not represent the official views of HP unless explicitly stated otherwise.

Received on Wednesday, 5 March 2008 07:05:11 UTC