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

[Drummond Reed <drummond.reed@xdi.org>]

Following are the minutes of the unofficial telecon of the XDI TC at:

Date:  Thursday, 07 January 2010 USA
Time:  1:00PM - 2:00PM Pacific Time (21:00-22:00 UTC)

ATTENDING

Bill Barnhill

Markus Sabadello

Drummond Reed

Giovanni Bartolomeo

1) $HAS ASSOCIATIVITY

See the thread started by Giovanni at:

  http://lists.oasis-open.org/archives/xdi/201001/msg00011.html

and the response from Drummond at:

  http://lists.oasis-open.org/archives/xdi/201001/msg00012.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.

 

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.

 

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 document.

 

We ran out of time, and did not resolve the underlying issue about $has associativity, so we agreed to continue discussion in email and on next week's call.


2) NEXT CALL

Next week at the regular time.