W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > June 2001

Re: (tentative) container model proposal

From: pat hayes <phayes@ai.uwf.edu>
Date: Wed, 20 Jun 2001 15:57:36 -0500
Message-Id: <v0421010bb756bbb3bc81@[205.160.76.183]>
To: Dan Brickley <danbri@w3.org>
Cc: w3c-rdfcore-wg@w3.org
> > > My claim was pretty modest: just that both rdf:type and rdf:_n 
>constructs
> > > are similarly privileged in RDF's XML syntax, but that neither deserve
> > > any special architectural privilege w.r.t. the basic formalities of the
> > > triples model. Whether we feel the one is more/less useful, intuitive etc
> > > is a separate issue, and one that you're right to postone to future work
> > > on syntax beautification.
> > >
> > > Dan
>
> > Amen. Stated differently, everything not in the first box
> > in section 5 of the M&S spec should go away from the spec
> >
> > guha
>
>(that's a little stronger, but i think we basically agree...)
>We don't want it all to go away, just to "go away" from that (central,
>foundational) section of the spec. As DanC
>noted last week, there are some constraints, such as that being the 
>n-th member
>of a container is a uniquely identifying property (ie. that each
>rdfs:ContainerMembershipProperty is a daml:FunctionalProperty ((?)),

I must have missed that. Surely that doesn't make sense for bags? 
Being the n-th item in a bag, if it means anything, can only mean 
being the n-th item in some representation of the bag. But another, 
different, representation of the same bag might have that element in 
a different place.

All data structures are ordered, in a sense, if only by the address 
structure of the memory hardware.  So unordered structures like bags 
are idealisations which can be formally defined as equivalence 
classes of ordered structures over re-orderings. Which is a fancy way 
of saying that two 'unordered' structures that differ only in their 
ordering (ie they are encoded as two different ordered structures and 
you can get one of these from the other by reordering it) are 'the 
same' unordered structure.

If structures are uniquely identified by the order of their elements, 
then they aren't unordered, period. So they aren't bags. Of course, 
we can call them rdf:Bag if we like, but then all we are doing is to 
add to the general air of confusion.

Pat Hayes

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Received on Wednesday, 20 June 2001 16:57:41 EDT

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