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Re: Comments on informal meaning of the RDFS vocabulary

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Thu, 30 Jan 2003 10:39:38 -0500 (EST)
Message-Id: <20030130.103938.88040053.pfps@research.bell-labs.com>
To: bwm@hplb.hpl.hp.com
Cc: www-rdf-comments@w3.org

From: Brian McBride <bwm@hplb.hpl.hp.com>
Subject: Re: Comments on informal meaning of the RDFS vocabulary
Date: Wed, 29 Jan 2003 22:12:15 +0000

> At 16:03 29/01/2003 -0500, Peter F. Patel-Schneider wrote:
> 
> [...]
> 
> > >
> > > >The implementor may decide that RDF
> > > >lists have unique firsts and rests and write an RDF system 
> > accordingly.  The
> > > >user may believe that RDF lists must always have unique firsts and rests.
> > >
> > > That is clearly the design centre.  What text in the schema doc is
> > > incorrect[?]
> >
> >The following text (emphasis added)
> >
> >         5.2.2 rdf:first
> >
> >         rdf:first is an instance of rdf:Property that is used to indicate
> >         *the* first item of a list.
> 
> Ha!  Phrases including the words "hoist" and "petard" come to mind unbidden :)
> 
> Can I find more wiggle room here than there is around owl:Class?
> 
> The text here is not false.  

It certainly is misleading, which might even be worse here.

> rdf:first is used to indicate *the* first item 
> of a list, i.e. where the list is "well formed".  The text does not 
> preclude the list not being "well formed".
> 
> Might your concern be addressed if the text were modified to include a 
> discussion of well formed and not well formed lists.  I'd probably need 
> some help with the wording, but something along the lines of:
> 
> [[
> A rdf:List is well formed if it meets either of the following conditions:
> 
>    o it is rdf:nil
>    o - it has exactly one rdf:first property,
>      - and it has one rdf:rest property
>      - and the value of its rdf:rest property is a well formed list.

This is not sufficient to describe well-formed lists!  (Think of infinite
or circular lists.  Also think of what happens if rdf:nil is the subject of
a triple whose predicate is rdf:first or rdf:rest.)

> This section describes the meaning of well formed lists.  Whilst an RDF 
> graph may contain lists that are not well formed, this is strongly 
> discouraged and the meaning of such lists is not described in this document.
> ]]

Well, if you are going to do this, you should also include a similar
discussion of RDF containers and rdf:Statement.

> Brian


peter
Received on Thursday, 30 January 2003 10:40:05 GMT

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