W3C home > Mailing lists > Public > public-awwsw@w3.org > November 2008

RE: statements about resources vs. representations

From: Booth, David (HP Software - Boston) <dbooth@hp.com>
Date: Wed, 26 Nov 2008 03:44:48 +0000
To: Jonathan Rees <jar@creativecommons.org>, Pat Hayes <phayes@ihmc.us>
CC: "public-awwsw@w3.org" <public-awwsw@w3.org>
Message-ID: <CD2B872281385A439B98164F5351E6DD39C44ECCFC@GVW1144EXB.americas.hpqcorp.net>

> From: Jonathan Rees
> [ . . . ]
> described in http://www.w3.org/DesignIssues/Generic.html ?
> fftr:IR (David Booth) - mathematical mapping from Request x
> Time to Response
> [ . . . ]
> I'm not sure how fftr:IRs relate to Accessibles. Again, I think the
> classes are disjoint, since I'm not sure how I'd get a causal pathway
> to a function.

Okay, well, let's assume that "accessible" means that a representation is likely to be retrievable.  And to make that more concrete, let's define "likely to be retrievable" as "was available in the last 24 hours".  Then we could say:

 :AccessibleIR rdfs:subClassOf :InformationResource .

And a rule could say something to the effect that "if there exists an :InformationResource ir with a representation that was retrieved less than 24 hours ago, then ir is a :AccessibleIR".

>
> httpRange-14 permits one to use http: URIs to name things that aren't
> allowed by RFC 2616, but says that any 2xx-responder ought to be an
> AWWWIR. However, incorrect use of the http: scheme so extended can
> result in non-AWWWIRs that are 2xx-responders (e.g. Dublin Core URIs).

I don't think that's quite the right perspective.  I think if a GET on a URI yields a 2xx response, that is conclusive evidence that the URI *does* denote an IR, regardless of anything else that the URI owner may state through other means.  If the URI owner also declares through other means that the URI denotes Dan's car, then there is a URI collision:
http://www.w3.org/TR/webarch/#URI-collision
Another term for URI collision is "ambiguity", for example, when a single URI http://markbaker.ca/ denotes both Mark Baker the person and Mark Baker's web page.  As pointed out on slides 19-20 of
http://dbooth.org/2008/irsw/slides.ppt
this is architecturally identical to the problem that occurs when a URI for the protein AKT is minted, and AKT is later discovered to be three distinct proteins: AKT1, AKT2 and AKT3.  And as Pat Hayes has pointed out many times, this kind of ambiguity will never be eliminated.  Fortunately, such ambiguity is not a show stopper, because: (a) the ambiguity may not matter to many applications; and (b) when the ambiguity does matter, the ambiguous URI can be related to more specific URIs, using skos:narrower.

>
> But all that aside... one question I have is whether the classes
> Edition and Accessible intersect.

Strictly speaking, no.  But that won't stop people from using the same URI to denote both.  That's the ambiguity mentioned above.

Ambiguity is a fact of life, and Semantic Web practitioners just have to get used to it.  This does *not* mean that I condone sloppiness!  Rather, it means that ambiguity is unavoidable, and what one person may view as good enough (and *unambiguous* to one application), another may view as sloppy (and *ambiguous* to another application).

I personally think these architectural questions become a *lot* easier to answer if one makes a few of simple assumptions about Semantic Web architecture:

 - an InformationResource is essentially a function from (Time x Request) to Representation; and

 - a URI denotes a resource through a two-step mapping from URI, to a set of assertions, to the resource, as described in
http://dbooth.org/2008/irsw/slides.ppt

However, maybe I'm just a broken record.  :)



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

Statements made herein represent the views of the author and do not necessarily represent the official views of HP unless explicitly so stated.
Received on Wednesday, 26 November 2008 03:46:13 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Wednesday, 26 November 2008 03:46:15 GMT