[xdi] Minutes: XDI TC Telecon Thursday 1-2PM PT 2010-01-07

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

Dear Drummond,

In order to be very clear, could you please distinguish between  
proposals and agreements? Some suggested changes to your notes are  
below.

Kind Regards,
Giovanni

> 1) $HAS ASSOCIATIVITY
>
> See the thread started by Giovanni at:
>
>    
> http://lists.oasis-open.org/archives/xdi/201001/msg00011.html<http://www.oasis-open.org/committees/download.php/35421/xdi-rdf-box-graphs-v1.pdf>
>
> and the response from Drummond at:
>
>   http://lists.oasis-open.org/archives/xdi/201001/msg00012.html
>
>

For the sake of completeness, please check also the following of this thread:

http://lists.oasis-open.org/archives/xdi/201001/msg00014.html
http://lists.oasis-open.org/archives/xdi/201001/msg00019.html
http://lists.oasis-open.org/archives/xdi/201001/msg00022.html

>
> We began discussion by revisiting some of the decisions we made about the
> $has operator last spring.
>
>
>
> # ACTION: Drummond will look for an email or minutes that he sent last
> spring about deciding that $has$a still had a role.
>
>
>
> We then progressed into talking about the nature of $has relationships, and
> Drummond's assertion that from an RDF standpoint, a $has statement does not
> actually assert that an RDF graph node has an outgoing RDF graph arc. That's
> the job of a $has$a statement, and the reason that only $has$a statements,
> and not $has statements, can have cardinality.
>
> So what Drummond explained is that $has statements do not assert that the
> $has object is an outgoing arc from the $has subject, only that the $has
> object is a valid outgoing arc for the $has subject. The reification of the
> relationship between the $has subject and the $has object, for example
> reifying +a/$has/+b into (+a/+b), creates a new XDI RDF subject +a+b.
>
>

Please note that during the conference we DID NOT AGREE on this  
concept. Current specs  
(http://wiki.oasis-open.org/xdi/XdiOne/RdfGraphModel) says:

"$has describes the relationship between a node and an outgoing arc in  
the XDI RDF graph. The subject of a $has statement is the XRI of the  
node from which the arc originates, and the object is the XRI of the  
arc."

Bill pointed out that +a/$has/+b implies +a/+b and viceversa, i.e.  
they are logically equivalent statements.

> This led us into a discussion of the relationship of XDI RDF graphs and
> conventional RDF graphs. For example, the XDI statement +a/$has/+b diagrams
> as a normal subject/predicate/object triple in an XDI RDF graph. But when
> you convert that statement into what it describes in a conventional RDF
> graph, it translates into a single RDF subject node identifier,  
> +a+b. This RDF node "contains" the XDI RDF graph +a/$has/+b, but  
> that is transparent to
> conventional RDF, because conventional RDF does not have the notion of
> contexts, i.e., graphs as objects of other graphs.

Please note that during the conference we DID NOT AGREE on any notion  
of "containment" above suggested.

What we agreed during last Spring (reported in  
http://lists.oasis-open.org/archives/xdi/200904/msg00021.html):

#1:        +x/$has/+y        INFERS:

             +y/$is$has/+x
             +x+y/$is$a/+y
             +y/$a/+x+y
             +x+y
             +x/+y

The corollary is also true, i.e.:

#1A:     +x+y                 INFERS

             +x/$has/+y
             +y/$is$has/+x
             +x+y/$is$a/+y
             +y/$a/+x+y
             +x/+y

>
> That led us to discussing the challenge of converting XDI RDF graphs into
> conventional RDF graphs (and XDI RDF documents into conventional RDF
> documents) because of the issue that XDI contexts has no equivalent in RDF.
>
> Bill explained that the way he is currently doing it is taking the XDI RDF
> graph, and converting it into a set of conventional RDF graphs containing
> statements referring to other RDF graphs using named graphs. Using this
> approach, all but the most trivial XDI RDF statements will require at least
> two conventional RDF graphs to express, and some of them may require dozens,
> as indicated by examples in the XDI RDF Box Graphing
> <http://www.oasis-open.org/committees/download.php/35590/xdi-rdf-box-graphs-v2.pdf>
> document.
>




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