Minutes: XDI TC Telecon Thursday 1-2:00PM PT 2011-01-06

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

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

Date:  Thursday, 06 January 2011 USA
Time:  1:00PM - 2:30PM Pacific Time (21:00-22:30 UTC)

ATTENDING

Joseph Boyle
Markus Sabadello
Drummond Reed
Giovanni Bartolomeo
Michael Schwartz


THE GOTOMEETING FOR TODAY IS:
     https://www2.gotomeeting.com/join/969244355

THE IDEARPAD LINK FOR TODAY IS:
     http://xdi.idearpad.org/17


1) GIOVANNI'S SLIDES ABOUT URI AND XRI EQUIVALENCE

Giovanni uploaded a PDF about this before Christmas. See:

   http://lists.oasis-open.org/archives/xdi/201012/msg00025.html 
   http://www.oasis-open.org/committees/download.php/40647/equivalence-xri-uri-2010.pdf
   
Giovanni walked through the four bullets in the presentation.
 * The first point is to declare a standard way to express any URI as an XRI using a cross-reference. 
 * The second point is establishing equivalence between the URI and XRI using an XDI statement. Giovanni's slide uses the $is predicate and proposes the same semantics as owl:sameAs. Giovanni noted that other OWL concepts can be "imported" into XDI in this way. Drummond agreed, noting only that if we use the metagraph symbol proposal (http://wiki.oasis-open.org/xdi/MetagraphSymbols), the equivalence predicate would be $ instead of $is.
 * The third point is about how to convert an XRI into a URI -- the inverse of the first point. This is now a fundamental premise of the XRI 3.0 Syntax spec (http://www.oasis-open.org/committees/download.php/35972/xri-syntax-3.0-wd03.pdf).
 * The fourth point is the most important from an ontology standpoint -- it allows XRIs to be used inside conventional RDF documents. This Turtle statement asserts equivalence between an XRI and a URI. This could provide a way to "bridge" between XDI graphs and conventional RDF graphs.

Drummond pointed out that in the fourth bullet, the unbound XRI is "+person", so the RDF statement should be xri:+person. Giovanni will update this.

Drummond also noted that while it is now clear how you can express XDI graphs as RDF graphs, you cannot (at least any way we have discovered yet) express all the XDI metagraph semantics in RDF. But you can show that XDI graphs are backwards compatible with RDF graphs and XRIs can be expressed as URIs and vice versa.

We then talked about the first bullet, and the use of a cross-reference without a global context symbol. Drummond explained why he now believes it is semantically acceptable to use a pure cross-reference to identify the root node of an XDI graph. This has to do with increased clarity of semantics pertaining to cross-references, about which he plans to publish another wiki page soon.


2) DISCUSSION OF XDI DICTIONARY PATTERNS

Based on the action items in our December  23 call, Drummond produced an example XDI dictionary corresponding to a  number of the patterns we have been discussing on the http://wiki.oasis-open.org/xdi/XdiGraphPatterns page. See:

   http://wiki.oasis-open.org/xdi/XdiDictionaryPatterns

Drummond gave a brief tour of the major patterns in the dictionary, after warning that it contains a large amount of information and key patterns.

Giovanni's first observation was that it is not common for RDF ontologies to be used as data definition languages. Drummond said that one of the core features of XDI dictionaries is to be able to use one grammar to describe semantic relationships of all types, from the most granular data definitions to the most general semantic statements about people, organizations, and concepts.

Drummond pointed out the example near the end of the dictionary of how an address (postal or delivery) is semantically described with great precision, and contextualized for different countries.

At this point Giovanni said that some properties of the address structure might be confused with corresponding real world concepts; for example, +country is a string in the context of the address structure Drummond illustrated, but could represent the class Country, i.e. the class identifying the Countries of the world. These are two different things. Then we discussed how important is to have a way to contextualize at a glance subsegments appearing in an XRI inside a XDI. In RDF (and XML) prefixes are used (owl: foaf: etc.) to give at a glance the indication of which context the term refers to.

Mike would like to focus on a specific set of use cases that he would like to see developed, and will post that as a wiki page before the next call.

3) NEXT CALL

The next call is next week at the regular time.

------------
ONGOING ISSUES LIST

Each of these is a candidate for the agenda for future calls.

* PROPOSED CONSTRUCTS/OPERATORS FOR XDI

Discuss the following wiki page originally posted by Giovanni:

  http://wiki.oasis-open.org/xdi/XdiNewFoundation

* DICTIONARY STRUCTURE

Mike would like an example of the PDX dictionary as soon as we can do it.

*   EQUIVALENCE SEMANTICS

Close on whether we need an additional $ word that is the equivalent
of Higgins Personal Data Model (PDM)  semantics   of h:correlation,
which is not as strong as $is.

      http://lists.oasis-open.org/archives/xdi/201006/msg00036.html

* COOL URIS

Continue previous discussion about the use of standard RDF URIs in XDI:

  http://lists.oasis-open.org/archives/xdi/201006/msg00023.html