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Re: Reification as nesting

From: Drew McDermott <drew.mcdermott@yale.edu>
Date: Fri, 8 Jun 2001 11:22:29 -0400 (EDT)
Message-Id: <200106081522.f58FMTi29057@pantheon-po02.its.yale.edu>
To: www-rdf-logic@w3.org

   [Drew McDermott]
   >I find etc dubious, too.  The traditional way to introduce
   >multi-argument functions into RDF would be to write
   >   [statement33 rdf:type love_triangle]
   >   [statement33 winner melanie]
   >   [statement33 won ashley]
   >   [statement33 loser scarlett]
   >rather than
   >   [love_triangle scarlett [etc melanie ashley]]

   [Pat Hayes]
   Yes, that is the more traditional RDF approach, along the lines of 
   how it handles containers; although if the RDF M&S is taken 
   seriously, then  'statement33' would be better written 'event33' or 
   'fact33' or something like that. However, this approach, if carried 
   through rigorously, would mean that a simple 'naive' RDF triple 
   assertion [s V  o] should also get the same treatment, ie it should 
   be rewritten in the form
   [fact19 rdf:type V]
   [fact19 somethingLikeSubject s]
   [fact19 somethingLikeObject o]

I don't think this is any more "rigorous"; it might be more
consistent, but I think most semantic-net hackers have been willing to
treat binary relationships differently from n-ary relationships.

   [Drew McDermott]
   >It is indeed impossible (or highly artificial) to give [etc melanie
   >ashley] a coherent meaning.

   [Pat Hayes]
   I think you mean, to give it a coherent meaning in isolation, ie out 
   of context, right? But that is precisely what I would not want to do. 
   The current RDF model in which every triple must have a full RDF 
   meaning regardless of its context is precisly what I am trying to get 
   past, since it makes it impossible to express more complex syntax 
   within RDF (without cheating of one kind or another.)

   When we use triples to implement more complex syntax, some of 
   them ARE terms. Some of them, in fact, are not even fully-fledged 
   syntax of any kind, but are only pieces or fragments of larger 
   well-formed expressions I see no harm in this as long as we can 
   clearly recognise such things. In this scheme they are precisely the 
   ones that start with 'etc'.

I don't think it's specifically an RDF requirement that every
subexpression must have a "full ... meaning"; it's just compositional
semantics.  If [etc a b] is not a subexpression of [R c [etc a b]],
then we should just admit we're allowing n-ary relations into the
language, and go to [R c a b].

I agree we need terms in RDF.  But declaring that some "triples" are
terms, or fragments of terms, seems like too big a departure from the
current language.  For a triple to be a triple in the current sense,
it must be an assertion (or be an assertion when bindings of its free
variables are supplied).  Any term that isn't of the form
predicate(a,b) should be dealt with by describing it in terms of
triples.  We can always provide syntactic sugar that allows a more
concise representation for human consumption.

                                             -- Drew McDermott
Received on Friday, 8 June 2001 11:22:37 UTC

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