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Re: graphs are sets?! (was: rdfms-difference-between-ID-and-about (was: Issues list update/status?))

From: Jan Grant <Jan.Grant@bristol.ac.uk>
Date: Fri, 5 Oct 2001 16:45:27 +0100 (BST)
To: Pat Hayes <phayes@ai.uwf.edu>
cc: w3c-rdfcore-wg <w3c-rdfcore-wg@w3.org>
Message-ID: <Pine.GSO.4.31.0110051641410.3948-100000@mail.ilrt.bris.ac.uk>
On Fri, 5 Oct 2001, Pat Hayes wrote:

> >On Thu, 4 Oct 2001, Aaron Swartz wrote:
> >
> >>  On Thursday, October 4, 2001, at 09:34  AM, Jeremy Carroll wrote:
> >>
> >>  > I would prefer test1.nt to only have one line if they are
> >>  > identical. The
> >>  > graph is a set.
> >>  > A comment explaining the deletion would then be helpful.
> >>
> >>  Whoa, whoa, whoa, I don't think we ever agreed to this. It was
> >>  my understanding the output was a bag (there wasn't harm in
> >>  doing so), but could be interpreted as a set.
> >>
> >>  When was this changed?
> >
> >The MT would give the same interpretation for equivalent arcs in a
> >multigraph, wouldn't it?
>
> Yes, in fact RDF graphs are multigraphs. However, that means that the
> MT works just as well if they are sets or bag. Bags is semantically
> harmless and puts a lighter burden in implementers, so I would vote
> for bag.

Sets are semantically harmless too and put a lighter burden on me as an
implementer :-) , so I'd rather do the following:

- treat rdf storage systems as sets (maybe, unless they do something
groovy with provenance)
- warn consumers of TripleIterator streams that they may see the same
statement more than once
- and so on.

In other words, the behaviour of an application over time as assertions
and retractions are made is a decision that the application-writer has
to make and advertise to his users.

jan


-- 
jan grant, ILRT, University of Bristol. http://www.ilrt.bris.ac.uk/
Tel +44(0)117 9287088 Fax +44 (0)117 9287112 RFC822 jan.grant@bris.ac.uk
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Received on Friday, 5 October 2001 11:47:53 EDT

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