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Re: "tdb" and "duri" URI schemes...

From: Jonathan Rees <jar@creativecommons.org>
Date: Wed, 3 Nov 2010 12:05:53 -0400
Message-ID: <AANLkTi=gP2mxWrnQ9VY6o9x+kaBO=zhqZ-wfvWvCv7T0@mail.gmail.com>
To: nathan@webr3.org
Cc: Larry Masinter <masinter@adobe.com>, "www-tag@w3.org" <www-tag@w3.org>
Just to be clear, the goal here, I think, is not to argue for or
against tdb: or duri:. The problem to be solved is that people are
talking about duri: and tdb: but don't have a good publication to cite
that describes them. Right now we should be focussing on how to help
Larry publish the clearest document possible as a contribution to the
larger conversation about "identifiers".

On Wed, Nov 3, 2010 at 10:42 AM, Nathan <nathan@webr3.org> wrote:
> so in an n3/turtle version of the above, should I be using tdb's or duri's
> and in which combination? what are the consequences of using the wrong ones?

I know how Larry feels about RDF, so I'll try to answer for him.

The semantics of tdb: is pretty clear, I think: expressed in RDF we have
    <duri:T:U> foaf:primaryTopic <tdb:T:U>.
(For those of you who have as much difficulty with the role-noun
pattern as I do, '-- foaf:primaryTopic --' should be read '-- has, as
its primary topic, --'.  http://xmlns.com/foaf/spec/#term_primaryTopic
)

The semantics of duri: is a bit more complex but also clear in
RDF-land I think.  The expression in RDF is awkward since it involves
the ternary relation "A is {what B was like at time T}". Rather than
invent the three necessary RDF properties I'll just write it that way.
   <duri:T:U> is {what _U1 was like at time T}
       where _U1 is {what U identified at time T}.
We don't usually reify the "identified by" relation in RDF, or worry
about changes in the relation over time, since there is little benefit
in doing so. If we thought that U "identified" two different things at
two times, we probably wouldn't want to call either of those things
<U>. For most purposes we can take <U> = _U1, and we have
   <duri:T:U> is {what <U> was like at time T}

You seem to be pretty good with RDF and reasoning, so you should be
able to figure out how to use tdb: and duri: based on the above
semantics.

If you're familiar with Memento, {what <U> was like at time T} should
look familiar. In an earlier email I expressed the relationship in
terms of "representations".

I'm not sure how to make the document say all this better than it
already does (beyond the suggestions I already sent). If you can
figure out where it's unclear that would be helpful.

It's not clear whether one can use duri: for things other than
"information resources". I would assume not, but I don't think
generalizing it to, say, physical objects (what my hand was like in
1976) adds any logical complexity. I don't think the document should
talk about this twist.

Jonathan
Received on Wednesday, 3 November 2010 16:06:22 GMT

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