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RE: Reification of Sets (of RDF Statement, for Queries)

From: Jan Grant <Jan.Grant@bristol.ac.uk>
Date: Tue, 10 Apr 2001 11:41:02 +0100 (BST)
To: Danny Ayers <danny@panlanka.net>
cc: Sandro Hawke <sandro@w3.org>, www-rdf-interest <www-rdf-interest@w3.org>
Message-ID: <Pine.GSO.4.31.0104101129460.14755-100000@mail.ilrt.bris.ac.uk>
On Tue, 10 Apr 2001, Danny Ayers wrote:

> <- Issue 1: RDF M&S Does Not Provide Sets
> <-
> <- The argument against them I've heard is "we don't have an enforcement
> <- mechanism" (for duplicates, so use bags) or "we have to provide them
> <- in some order" (so use lists).
> <-
> <- I think those arguments against defining a vocabulary for
> <- communicating information about set membership are, to put it mildly,
> <- weak.
> <-
> <- On the first point, you don't need to provide an enforcement
> <- mechanism.  If someone says "X contains 3" and then "X contains 3"
> <- again, well, you know "X contains 3".  No problem.
> IANAL, but don't we still need to be able to tell the difference between
> e.g. {1, 2, 3, 4} and {1, 3, 2, 3, 3, 3, 4, 3}?

What difference? They're both representations of the same set.

> There is definitely elegance to LISP-style lists, though personally I can't
> judge how appropriate they would be in this context - the RDF model is
> pretty much object-orientated (maybe transformed a little) - how well does
> the mix of lists & objects work in e.g. CLOS?

I was initially taken with this construct (I think pretty much everybody
has invented this as a notion as some point) but I'm less inclined to
like it now. Why? Weeeell, why not use something slicker, like balanced
trees? Or any other data structure of your choice?

I prefer the abstraction of just using numbered members. An RDF
implementation is free to use whatever datastructure it pleases behind
the scenes*; given a little API support, there need be no O(n) cost for
fetching the _n_th sequence member, etc.


* http://tribble.ilrt.bris.ac.uk/~cmjg/rdf/java/RDF.tar.gz for a
snapshot of an (in-progress) example of this, amongst other things.

jan grant, ILRT, University of Bristol. http://www.ilrt.bris.ac.uk/
Tel +44(0)117 9287163 Fax +44 (0)117 9287112 RFC822 jan.grant@bris.ac.uk
User interface? I hardly know 'er!
Received on Tuesday, 10 April 2001 06:43:03 UTC

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