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Re: Permanent model names in TKS/Kowari

From: Dan Connolly <connolly@w3.org>
Date: Sat, 20 Nov 2004 22:21:06 -0600
To: Tom Adams <tom@tucanatech.com>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Message-Id: <1101010867.27188.87.camel@dirk>
On Sat, 2004-11-20 at 23:04 -0500, Tom Adams wrote:
> Hi guys,
> Here is a summary of the discussions that we've been having internally 
> on permanent model names

There's that "model" word again... would you please rephrase
in Feb 2004 terminology? Do you mean RDF Graph?

or do you mean something mutable? (Graphs are immutable syntactic
things, like numerals and strings).

>  and ideas for a) how we name models and b) how 
> we separate model names from their access mechanism, there's also some 
> syntax at the bottom. For the record, a most of this discussion comes 
> from Andrew Newman. All comments are speculation, I don't believe we've 
> implemented these ideas as yet ;)
> Our discussions have been motivated by a number of reasons, a lot of 
> which have been coming to us from customers:
> o Models should to be named in order to be able to reference them in 
> queries;
> o Names should be independent of the method of access (i.e. protocol);

Not if you mean "model" in the sense of "mutable store" ala
"file" or "document".

And if you mean something immutable, it seems a lot simpler to use
a hash.

> o Names should be independent of the hostname of the machine they're 
> stored on;

Yes, but DNS names meet that criterium. (hint: which machine
is www.w3.org? Which continent, for that matter? A: many.)

> o Models should be able to be moved from machine to machine;
> o The content of a model may reside in a different storage mechanism 
> over time, e.g. RDF/XML file or TKS/Kowari model.
> Some other work has been done around similar things. @semantics did a 
> presentation on resolving models at the WWW2004 conference:
> http://www.asemantics.com/presos/devdays-2004/y-532x400-12.html
> There's a few RFCs that cover similar topics:
> DDDS part 3: http://www.ietf.org/rfc/rfc3403.txt
> DDDS part 4: http://www.ietf.org/rfc/rfc3404.txt
> Using HTTP in URN Resolution: http://www.ietf.org/rfc/rfc2169.txt
> Handle System Overview: http://www.ietf.org/rfc/rfc3650.txt
> So cutting to the crunch, TKS/Kowari currently use model names of the 
> form:
> protocol://hostname/servername#modelname
> For example:
> rmi://knuth.bne.tucanatech.com/server1#foo
> beep://knuth.bne.tucanatech.com/server1#foo
> This confuses two distinct properties of a model: the model name and 
> how to access the model.

I'm not at all sure that's the case.

> TKS/Kowari stores model information in a special place called the 
> system model. This model stores information such as the type of a 
> model, e.g. a full text model or a native "Tucana" model. As far as 
> Tucana is concerned, we want to solve the problems outlined above, but 
> also allow for backwards compatibility with existing queries. As we 
> want to be able to store model information in RDF, and make statements 
> about models, we need to use a resource to reference a model. We're 
> considering using URNs to name models.
> Our proposed new model naming scheme would use the system model to 
> contain information about the models including their name and how to 
> access them. So for example we could be storing the following triples:
> <urn:slashdot-org:news-rss> <access> <http://slashdot.org/news.rss>
> <urn:slashdot-org:news-rss> <updateEvery> <5 minutes>
> <urn:knuth-com:server1:foo> <access> <rmi://localhost/server1>
> <urn:tucanatech-com:server1:hr> <access> <rmi://localhost/server1>

Why not
  <http://example/someplace#slashdotNews> <access> ...

> The first model <urn:slashdot-org:news.rss> is an remote model that you 
> access using the given URL (http://slashdot.org/news.rss) and you 
> update it every 5 minutes.

Aha... so you _do_ mean something mutable.

>  The second and third models are local 
> models. The third model is a company model that you just happen to have 
> a local copy of.
> So now onto some syntax examples, feel free to tune out.

Please take a look at

  The Myth of Names and Addresses

and see if you still think urn: helps at all.

Dan Connolly, W3C http://www.w3.org/People/Connolly/
D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E

Received on Sunday, 21 November 2004 04:20:24 UTC

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