Re: XDI RDF addressing alternatives? (was RE: Minutes: XDI TCTelecon Thursday 1-2PM PT 2009-04-02)

["Giovanni Bartolomeo" <giovanni.bartolomeo@uniroma2.it>]

Hello Drummond,

Thanks for your mail. A clarification to your first concern: note that  
X3 is only the serialization format it is used to define new subjects,  
and it does not replace the graph. As I wrote:

...Using these compound identifiers, it is possible to *introduce in  
the XDI/RDF graph* five new nodes: @example.org+employee  
@example.org+ceo @example.org+employee=j.doe  
@example.org+employee=m.smith @example.org+ceo=r.walker which are not  
part of the original graph, but are useful to make entailments on the  
graph itself (metamodel)...

This means that the new nodes *are* actually new subjects in the  
graph, and they can appear as roots in the tree, when you make  
assertions about them. For example, you can have

@example.org+employee=m.smith
	+mail
		(mailto:m.smith@example.org)

thus you have two new nodes:

@example.org+employee=m.smith+mail
@example.org+employee=m.smith+mail(mailto:m.smith@example.org)

I've thought a bit about your second concern ("addressing capability  
of the XDI RDF graph is not something that can be expressed in
conventional RDF"). Well, I'm doing my best to investigate this and to  
try to remain inside RDF as much as possible.
Of course if we will find that something cannot really be really  
addressed, then it will make sense to shift to another model, but,  
this should be justified and supported by evidences. Otherwise we risk  
to reinvent things that already exist (and work!), and we risk our  
work to be not accepted by the scientific community (my biggest  
concern).

Kind Regards,
Giovanni

At 08.58 09/04/2009, Drummond Reed wrote:
Giovanni,

Thanks for making this posting. In reading through "A Different Proposal" at
the end, I am trying but have not yet been able to fully understand the
proposal. It appears that you are proposing that for the same X3 graph
rooted on the one XDI RDF subject, you are proposing that +x/+y addresses
one part of that graph (rooted on the +x subject) and +x+y addresses another
part of the same graph still rooted on the +x subject.

That seems to destroy the extensiblity model of the XDI RDF graph. You can't
actually create a new subject. As I understand the model you have written
up, you can't go beyond three levels, i.e., you can talk about +x, +x+y, and
+x+y+z. But what do you do about +x+y+z+j+k?

The $has verb in the proposed metagraph model in
http://wiki.oasis-open.org/xdi/XdiOne/RdfGraphModel is not limited to 2 or 3
levels deep. You can extend and create new XDI RDF subjects, predicates, or
objects to any depth.

The more I think about this topic, the more I believe that the addressing
capability of the XDI RDF graph is not something that can be expressed in
conventional RDF. It simply can't be done. It's like trying to express a
three-dimensional space in two dimensions. We are adding the dimension of
addressability to RDF graphs. It results in identifiers being combined into
new identifiers. RDF graphs have no such notion. I can't see any way around
it.

Thoughts? (We'll just have to continue the conversation in email this week
since I can't attend the XDI TC call tomorrow.)

=Drummond

> -----Original Message-----
> From: Giovanni Bartolomeo [mailto:giovanni.bartolomeo@uniroma2.it]
> Sent: Wednesday, April 08, 2009 5:23 AM
> To: xdi@lists.oasis-open.org
> Subject: RE: [xdi] Minutes: XDI TC Telecon Thursday 1-2PM PT 2009-04-02
>
> Hello,
>
> After our call of last week, I've updated today the XDIMetamodel page:
> http://wiki.oasis-open.org/xdi/XdiMetamodel
>
> Kind Regards,
> Giovanni
>
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