W3C home > Mailing lists > Public > www-rdf-interest@w3.org > August 2003

Re: practical problems with rdf:parseType="Collection" implementation

From: Sandro Hawke <sandro@w3.org>
Date: Thu, 14 Aug 2003 13:39:28 -0400
Message-Id: <200308141739.h7EHdSc9026563@roke.hawke.org>
To: www-rdf-interest@w3.org

> > There ought to be an official "memberOf" property with domain RDF:Resource
> > and range RDF:List that is true for each member of a list.  Implementers of
> > RDF servers might wish to implement such a property on their own, in hopes
> > that the (future) RDF committee will see the light and formally bless such 
> > a property some time in the future.

This was something dropped when DAML lists turned into RDF lists.  It
was raised as an OWL LC issue and closed to the raiser's satisfaction
[1].   Personally, I agree with your intuition on the matter.

> Yeah, I hoped there would be such a thing, it would have to be a
> property that couldn't be asserted manualy to prevent (partial)
> modification of the list structure, so thats pretty messy.

I don't see how list membership is different from pretty much anything
else in RDF.  Sometimes you add a triple; sometimes you remove a
triple.  Sometimes adding a triple makes your knowledge base
inconsistent unless you also remove certain triples.    For instance,
if you have

   # :list is the list ("a" "b")
   :list1 rdf:first "a".
   :list1 rdf:rest list2.
   :list2 rdf:first "b".
   :list2 rdf:rest rdf:nil.

and suitable rules, you could infer

   :list1 x:item "a".   
   :list1 x:item "b".   
and even
   NOT :list1 x:item "c".
assuming you had some kind of "NOT" operator.

If your user asserted (inserted):

   :list1 x:item "c"

you would hopefully say "No."  You might also say: do you want to make
this change:

   DELETE :list2 rdf:rest rdf:nil.
   INSERT :list2 rdf:rest :list3.
   INSERT :list3 rdf:first "c".
   INSERT :list3 rdf:rest rdf:nil.

... but that's just kind of a guess about what the user meant, and I
recommend against it.

Any notion of "change" in RDF, other than adding and removing triples,
seems very sketchy.

    -- sandro

[1] http://lists.w3.org/Archives/Public/public-webont-comments/2003Jul/0037
Received on Thursday, 14 August 2003 13:39:29 UTC

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