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RE: Is "Model" part of the RDF model?

From: McBride, Brian <bwm@hplb.hpl.hp.com>
Date: Fri, 20 Oct 2000 17:31:34 +0100
Message-ID: <5E13A1874524D411A876006008CD059FE7E076@0-mail-1.hpl.hp.com>
To: "'Arnold deVos'" <adv@langdale.com.au>, www-rdf-interest@w3.org
Arnold,

A good question.  I think the current situation is as you say
that model is not part of the the RDF Model.

I hope Sergey will respond with his views on the Stanford API.
Also relevant to this is the idea of contexts proposed by
Graham Klyne.  His paper can be found at:

  http://public.research.mimesweeper.com/RDF/RDFContexts.html

Jena's precursor was an implementation of a variant of the
Stanford API with a different approach to handling the URI's
of models.  It's models did have URI's and that was pretty
useful. I nearly did the same thing with Jena, but decided
I wanted to think about it a bit more and put that off
to a second release.  Jena in its current form is an
experiment to test out a style of API and is not yet final.

I don't think the API's use of models is a disguised attempt
to change the model.  I have suggested adopting a variant of
of the RDF Model which in which models are explicitly defined.

  http://lists.w3.org/Archives/Public/www-rdf-interest/2000Sep/0121.html


There is a clear need to be able manipulate collections of
statements.  Sometimes we want to serialize a particular
collection into a document, or do a query on a given collection
or make statements about a collection.

There seem to be two main approaches to doing this.  There can
be a concept of a collection of statements, i.e. a model aka
StatementSet.  Or there is only one universal model and RDF
itself is used to create collections of reified statements
within it, as bags or contexts.

In Jena's predecessor, models had URI's because I was
implementing a SQL based RDF store and I needed a way
to name different collections of statements.  It seemed
appropriate to use URI's and treating collections of
statements as resources enabled me to attach properties
to the collections.  In that regard, I think that those
models were very like what you are doing with bags of
statements.

One of the tasks on my todo list is to think about what the
Jena API would be like if it had no concept of model.

I think where I'm at at the moment, is that if model's exist
they should be resources.  But I'm still thinking about
whether they need to exist at all.

Brian






> -----Original Message-----
> From: Arnold deVos [mailto:adv@langdale.com.au]
> Sent: 20 October 2000 08:36
> To: www-rdf-interest@w3.org
> Subject: Is "Model" part of the RDF model?
> 
> 
> RDF API's Stanford [1] and Jena [2] seem to share the concept of a
> "Model" defined as a "container of triples" or "a set of Statements"
> respectively and not to be confused with *the* RDF model.
> 
> There is no explicit concept of a Model mentioned in the formal RDF
> definition [3], so my question is: is Model just an API mechanism or
> is it actually an extension to RDF in disguise?
> 
> I suspect the latter because the  distribution of statements among
> Model entities may influence the outcome of inferences and queries.
> For example, one might select among conflicting statements based on
> their provenance i.e. based on the Model that contains them.
> 
> Indeed, in the Stanford API the Model has a source URI so it can
> correspond to an RDF document. But again, is "document" a concept in
> the formal RDF model or is just part of the syntax?
> 
> In our in-house RDF engine we implemented "provenance" by reifying
> statements and putting them in a bag. Statements about the bag
> influence the credibility of the reified statements for the purpose of
> inference and queries.
> 
> In the Stanford API (but not Jena) the Model is-a Resource.  Is this
> resource intended to be the same as our bag?
> 
> Any insights into this would be helpful.
> Regards,
> Arnold
> ---
> Arnold deVos
> Langdale Consultants
> adv@langdale.com.au
> 
> [1] http://www-db.stanford.edu/~melnik/rdf/api.html
> [2] http://www-uk.hpl.hp.com/people/bwm/rdf/jena/index.htm
> [3] http://www.w3.org/TR/REC-rdf-syntax/#model
> 
> 
> 
> 
Received on Friday, 20 October 2000 12:31:51 GMT

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