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Re: RDF's Mixed-Mode Identifiers

From: Charles McCathieNevile <charles@w3.org>
Date: Fri, 3 Jan 2003 18:53:45 -0500 (EST)
To: Sandro Hawke <sandro@w3.org>
cc: <www-rdf-interest@w3.org>
Message-ID: <Pine.LNX.4.30.0301031840320.28167-100000@tux.w3.org>

On Fri, 27 Dec 2002, Sandro Hawke wrote:

>
>> I wonder if the answer is simpler.
>
>Yes, there are simpler answers, but they (as you put it) tend to fall
>down.  I haven't seen yet where my answer falls down.

Your answer falls down on the fact that there isn't an agreed standard yet
(which is, naturally, why you are proposing one). My approach falls down to
the extent that people say things in a way that is insufficently explicit.

To some extent that can be rescued by them being clearer - I am proposing a
practice that uses existing tools and syntax to clarify what is happening,
and can be partially rescued by adding domain/range information that could
clarify what is happening.

Perhaps it would make sense if your proposed properties were at a higher
level than the core specification - since it is more or less possible to make
sense of what is going on, and the proposal seems much more at the level of
OWL than further down, in practical application.

>And it's not that complicated: it's just that we need to distinguish
>between using a URI to talk about: (1) an information container, (2) the
>information it contains (if any), and (3) the subject (when there is one)
>of that information.  People freely go back and forth among these uses
>of URIs (mostly between the first two, which I didn't try to
>distinguish in my previous message, because it was less important),
>but for computers to do so is an enormous and unnecessary pain.
>
>> If EARL is talking about whether a web
>> page conforms to some content requirement then what you get at that web page
>> for a fragment is the thing under discussion.
>
>Hrm.  I'm confused.   The thing under discussion in the EARL report or
>in the web page?
>
>I'd guess EARL is talking about the content, here, by way of its
>container.  If the content at that URI changed (or was different for a
>different users), the EARL information would be wrong.  It's hard to
>talk about the content directly, unless you use a text string.
>Secure-Hash URIs really mask the difference, since the content and
>container are immutably bound.

This is an important issue in EARL (in my opinion at least). THe proposed
approach at the moment is to have an open property for identifying the
location within a page of a prolem, which allows us to use various addressing
schemes that are more or less robust over changes to the document (IDREF,
hashing a structure map, Xpointer, line/character offset have different
properties and levels of robustness against different kinds of modification),
and relevant information such as the context of a request for a specific
representation of a content-negotiated resource...

>> The problem case is when I want to talk about a thing that doesn't exist on
>> the web, such as my car, and make a claim in EARL that it conforms to the
>> roadworthiness standards of the state of Victoria (which also doesn't exist
>> on the Web).
>
>That's no problem for my approach: just allocate a container with that
>thing as its primary subject.

Well, it's no problem for either approach.

>> FOAF solves this problem by talking about "the thing that has a homepage at
>> http://example.net/foo" where 'has a homepage is unambiguous. This can be
>> used both for my car and the state of victoria (the publisher of a standard,
>> although the standard itself might actually be on the web).
>
>Yes, x:descriptionURIRef is very close to foaf:homepage.  But I think
>the notion of homepage is just a little too fuzzy, and easily confused
>with web site front pages, splash pages, one's personal "home" page in
>one's browser, etc.  So I tried to be more precise, and found myself
>prefering the reverse "primarySubject" arc for clarity.

The point I am trying to make is that foaf doesn't use a property on its own
- it says "the subject of this is a thing that has certain properties" thus
avoiding the problem without relying on a standardised property.

cheers

chaals
Received on Friday, 3 January 2003 18:53:46 GMT

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