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Re: Collections (Re: Misleading note about extensibiity ofCollection syntax)

From: Graham Klyne <GK@dial.pipex.com>
Date: Tue, 08 Aug 2000 15:53:25 +0100
Message-Id: <>
To: Pierre-Antoine CHAMPIN <champin@bat710.univ-lyon1.fr>
Cc: www-rdf-comments@w3.org
At 04:20 PM 8/8/00 +0200, Pierre-Antoine CHAMPIN wrote:
>Graham Klyne wrote:
> > >rdf:Bag
> > >-------
> > >(...)
> > I agree.  It might even be called rdf:Bag (i.e. syntax-compatible with the
> > current spec).
>Yes, keeping the class rdf:Bag (which is already a subclass of 
>rdfs:Container) ensures compatibility, so we must keep it. But since Bags 
>have no specificity w.r.t. Containers, that class is not useful anymore. 
>That's why I prefered using rdfs:Container.

Maybe.  I am thinking that the specific class might be useful for doing 
schema-aware processing, and beyond.  I am not trying to avoid using 
schemas, just not have parsing and graph-building dependent on them.

> > >rdf:Alt
> > >-------
> > >(...)
> > I don't agree here.  I think the term "choice" is unfortunate.  To me, it
> > simple implies a union type.  I would be happy with rdf:Alt and rdf:li, in
> > syntax and model.
>I think I see your point. So I think I would be happy too with rdf:Alt and 

... er, I'm now having some doubts about this.  I fear I may have confused 
*values* with *data types*.  (And I'm concerned the RDF M&S might have done 

As defined, rdf:Alt seems to represent a union data type, but rdf:Bag and 
rdf:Seq represent values.  A *value* of a union data type is just a single 

This might make some small sense if the collection classes are used to 
describe both data values, and  corresponding data types through some kind 
of template description approach.


    [<rdf:Bag>] --li--> [<Type>]

as a template for values like:

    [<rdf:Bag>] --li--> [value of <Type>]


    [<rdf:Alt>] --li--> [<Type1>]
    [         ] --li--> [<Type2>}

as a template for values like:

    [<rdf:Bag>] --li--> [value of <Type1>]
    [<rdf:Bag>] --li--> [value of <Type2>]

I'm not sure all of this is a good idea.  I think the problem is that 
<schema> wants a way to express Bag, Seq and Alt type values, but the RDF 
model itself only needs Bag and Seq.

> > >rdf:Seq
> > >-------
> > >(...)
> > Hmmm, interesting.  I'm not so sure about invoking reification in this
> > way.  I'll think about it some more.  Meanwhile, here are two other 
> approaches:
> >
> > (1) For an ordered list, I would be content to see "_1", "_2", etc. in the
> > syntax (rather than implied by the subject container class and rdf:li).
> >
> > (2) Use a LISP-like approach:
> >
> >      [<Cons>] --head--> [Item1]
> >      [      ]
> >      [      ] --tail--> [<Cons>] --head--> [Item2]
> >                         [      ]
> >                         [      ] --tail--> etc.
>The motivation behind the reification mechanism was illustrated in my 
>example :
>untill now, I only used Sequences when I needed an order between several 
>similar properties.
>I would like to avoid the trouble of having an intermediate node (the 
>Sequence resource),
>I'd rather like to specify that the order in the RDF serialization must be 
>kept in the model.
>Although reification is a bit cumbersome to handle, an appropriate API 
>could do that for me, anyway.
>Furthermore, that reification mechanism allows me to define Sequences as 
>we know them:
>simply the order of rdf:li properties.

I think I see where you are coming from.  There are attractions here.  If 
we can be confident that handling the reification won't become cumbersome 
then I could go with that.  I am hatching some ideas that might help.


Graham Klyne
Received on Tuesday, 8 August 2000 10:59:52 UTC

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