Special note about () in JSON serialization format

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

XDI TC Members:

Joseph pointed out today that although it's a very minor change, if anyone is already working in implementations of the JSON serialization format we worked out last fall, the revision from using the $ metagraph symbol as the key for statements about subcontexts to using the () metagraph symbol for this purpose is important. It has no practical implication other than being a different character in your code, but semantically it does make a real difference.

I agreed to send this special dedicated message in case you didn't read it in the minutes.

I have already updated the JsonFormat page on the wiki to reflect this change. There are no other changes (nor have there been since we reached consensus last fall.)

See also my next message about the open issue around literals, as this too is important for implementations being developed right now.

(A reminder that the OpenXDI Implementation call is tomorrow at noon PT -- the GoToMeeting link is https://www2.gotomeeting.com/join/969244355).

=Drummond

On Thu, Feb 10, 2011 at 8:29 PM, Drummond Reed <drummond.reed@xdi.org> wrote:

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

Date:  Thursday, 10 February 2011 USA
Time:  1:00PM - 2:30PM Pacific Time (21:00-22:30 UTC)

ATTENDING

Michael Schwartz
Drummond Reed
Joseph Boyle
Giovanni Bartolomeo


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

THE IDEARPAD LINK FOR TODAY IS:
     http://xdi.idearpad.org/22

Please try to preface each of your comments with your name so the
transcription into the minutes is easier.


1) XRI AND XDI RESOLUTION QUESTION

Mike asked about XRI resolution and XDI resolution. Specifically about a first use case :

XRI xri = new XRI("=schwartz");
XRIServiceEndPoint[ ] endPoints = xri.getServiceEndPoint();

Drummond explained that to use today's XRI resolution infrastructure, you must do XRI 2.0 resolution, and get an XRDS document. You can then put an XDI endpoint in that XRDS document and "switchover" to XDI.

But he said that as soon as Gluu wants to, it can bring up an XDI endpoint doing "XDI resolution", which is really just standard XDI $get calls for the URI representing the XDI endpoint for any XDI-addressable context. For example:

XDISubject subject = new XDISubject("=schwartz")


2) NEW DOCUMENTS: XDI GRAPH PATTERNS AND XDI GRAPH MODEL

Drummond uploaded documents that illustrate the full set  of basic patterns using the XDI graph model as explained in Giovanni's last document. The first is a set of visual graph diagrams showing the  patterns for simple properties, complex properties, simple subjects,  complex subjects, link contracts, and messages.

  PDF: http://www.oasis-open.org/committees/download.php/41091/xdi-graph-patterns-2011-02-09.pdf
  PPTX: http://www.oasis-open.org/committees/download.php/41090/xdi-graph-patterns-2011-02-09.pptx

The second is an update to what used to be the XDI RDF Model  document, now just titled the XDI Graph Model, that includes the  metagraph symbol vocabulary:

  PDF: http://www.oasis-open.org/committees/download.php/41089/xdi-graph-model-2011-02-09.pdf
  DOC: http://www.oasis-open.org/committees/download.php/41088/xdi-graph-model-2011-02-09.doc

We started our review on the first document above.

Giovanni had a question about the use of the ! suffix to distinguish a predicate that identifies a literal. Drummond explained that this rule satisfies a practical need for XDI processors to be able to identify the address of a literal. This would apply whether the literal is encoded as an XRI or not.

Giovanni felt that the datatype represented by an XRI predicate should be referenced in a dictionary entry.

Drummond agreed but said that this additional "metatyping" information at the address level has another advantage: using the ! suffix provides the option for XRIs that can identify both the literal form and the XRI form of some data. For example, a date in literal form could be addressed as $d!, and in XRI form could be addressed as $d.

Giovanni suggested that the question of whether a ! suffix was required or not for addressing a literal should be an open issue that can wait until we first decide whether all literals can (or must) be encoded as XRIs. We discussed this briefly that there could be a  great number of benefits to treating all literals as contexts. In  addition, it is trivial to turn a literal context into an actual  literal.

Drummond will add this to the open issues list.

Drummond next ran through the simple property pattern, explaining how metadata is applied, and also how versioning is applied.

We discussed the difference between the proposal to use !1, !2, !n and using $1, $2, $n. Giovanni has had a specific semantic proposed for $n, which is that they are used for defining synonyms for the elements (properties or objects) that appear, in a given document, under the context they are applied to. Example:

=bob
   +friend
     =alice
     =trudy
   +age
     "33"

=bob$1 is a synonym of =bob+friend, =bob$2 is a synonym of =bob+age; =bob+friend$1 is a synonym for =bob+friend=alice,  bob+friend$2 is a synonym for =bob+friend=trudy.

Drummond pointed out that this will only work if the $numbers represent document order, because the XDI graph (like RDF graphs) is inherently unordered. However if the semantics of $n are defined to mean document order, that will work. This also means that *numbers can be used to express explicit ordering within the graph itself ("graph order").

Drummond noted that in his versioning examples, the version instances should be using *numbers for explicit ordering. He will make that change.

3) TINY BUT IMPORTANT REVISION TO THE JSON SERIALIZATION FORMAT

In  doing the documentation above, Drummond realized that the metagraph  symbol () should have been used instead of $ for serializing subcontexts  in the JSON serialization format. Originally it looked like either $ or  () could have been used, and $ seemed to make more sense. However as  the semantics of the metagraph symbols are becoming more rigourously defined, it is now clear that () is not only semantically accurate but  and solves one key semantic problem we would have had with using $.  We'll discuss on the call to make sure there is consensus on this.


4) NEXT CALL

The next call is next week at the regular time. Drummond hopes to have another major chunk of documentation completed and posted before that call.



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

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

* STATUS OF XDI LITERALS

Should we force all literals to be encoded as XRIs, thus turning them into contexts?

* 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