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Re: Proposed issue resolutions

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Tue, 6 Nov 2001 12:31:59 -0600
Message-Id: <p0510103db80dda097b87@[65.212.118.166]>
To: Dan Connolly <connolly@w3.org>
Cc: w3c-rdfcore-wg@w3.org
>
>>  Propose close
>>
>>     http://www.w3.org/2000/03/rdf-tracking/#rdf-formal-semantics
>>
>>  on the grounds that the model theory adequately addresses this issue.
>
>Hmm... no, don't close that one; in particular, we haven't
>answered
>   When are two bags the same?
>cf recent comment from Massimo
>...
>crap; he didn't send it. Basically: I think that
>
>	_:b rdf:type rdf:Bag.
>	_:b rdf:_1 "abc".
>	_:b rdf:_2 "def".
>
>entails
>
>	_:b rdf:type rdf:Bag.
>	_:b rdf:_2 "abc".
>	_:b rdf:_1 "def".
>
>and generally: the _n arcs of a bag can be permuted.

That doesn't work. If it entails that, then it must also entail:

	_:b rdf:type rdf:Bag.
	_:b rdf:_1 "abc".
	_:b rdf:_2 "def".
	_:b rdf:_2 "abc".
	_:b rdf:_1 "def".

so just saying 'can be permuted' isn't enough. The fact is that we 
really shouldn't have indexed selectors on things that are supposed 
to be bags, since once you use those selectors once, the bag is 
ordered, whether you like it or not. You can only 'permute' it if you 
have state, and RDF has no states to permute over. Monotonic 
inference only adds conclusions, it can't do things like permutation.

>(Sorry, Pat, for all the times I said "containers
>don't have any other semantics." Massimo pointed
>out to me that Bags do. He claimed Alt does too,
>but I'm not convinced of that.)

Massimo is right.  rdf:Alt is a real can of worms, if we take it 
seriously; it breaks the basic core semantic model by introducing 
disjunction. (I had a strong sense at the F2F that rdf:Alt was dead 
meat; I hope I was right. If we keep rdf:Alt I will need to re-do the 
MT from the ground up. )

BTW, this issue shouldn't be closed in any case since the MT doesn't 
cover reification yet.

Pat
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Received on Tuesday, 6 November 2001 13:31:57 EST

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