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Subject: Re: [xdi] notes from meeting in Nice, Jan 29 2009
Hello Markus, thank you very much for having attended the event and
presented the Higgins project and its demo.
Thanks as well for the subsequent face to face discussion on relevant
XDI issues. I think it has been really productive. Your minutes are
very good and clear, hope these ideas could be a good input for the
ongoing works in the TC.
Kind Regards,
Giovanni
PS: Hope the French strike didn't cause you so many troubles in coming
back to Vienna!
At 03.15 30/01/2009, Markus Sabadello wrote:
Hi Giovanni (and others),
I'm trying to summarize in a few words what we talked about. Please
correct me if I made a mistake or forgot anything.
- We had a look at the xdi-rdf-global-graph-proposal-v1 which Giovanni
posted about a week ago:
http://www.oasis-open.org/committees/download.php/30802/xdi-rdf-global-graph-proposal-v1.pdf
- The basic graph model described in that document is essentially the
same as the one we are all familiar with (i.e.
subject/predicate/object triples), but the document proposes a new
methodology for drawing the graph. The main innovation is to draw
EVERYTHING that has an XRI as a node (including predicates!). Arcs are
drawn between the nodes, but arcs themselves don't have XRIs. A
typical statement consisting of subject, predicate and object would be
drawn as three nodes and three arcs.
- Arcs are colored to indicate which statement they belong to.
- A node with a given XRI never appears twice in the graph, but it can
of course be part of more than one statement. For example if you have
the following two statements:
=markus/+email/'markus.sabadello@gmail.com'
+email/$is$a/+contactdata
Then only a single node with the XRI +email would be drawn, but it
would be part of both statements.
- Giovanni distinguishes between Syntactic Correctness and Semantic
Consistency
- Syntactic Correctness simply means that the graph properly fits into
the RDF graph model (subject/predicate/object). This is a similar
concept to a "well-formed" XML document.
- Semantic Consistency means that the statements in the graph are
consistent with accompanying dictionary statements. E.g. if you have a
statement =markus/+friend/=giovanni, then for the graph to be
"semantically consistent", there would also have to be the dictionary
statement =markus/$has$a/+friend. These dictionary statements could be
mixed into the same graph, or they could exist in a separate document
or XDI endpoint (such as a Community Dictionary Service). This is a
similar concept to a "valid" XML document.
- The XDI Validator application could be extended to support
validating this Semantic Consistency.
- If you want you can work with XDI without caring about "semantic
consistency" / dictionary entries, just like you can work with XML
without caring about schemas / DTDs.
- Giovanni's document also introduces the concept of "roots", which
are drawn as a slash in a box. Those roots and the arcs originating
from them do not actually appear as statements in the graph, but they
indicate who is authoritative for an XRI. For example, all + XRIs
(+friend, +email, etc) come from the same "root" (the Community
Dictionary Service). Similarly, all $ XRIs ($is, $has, etc) come from
the same "root" (the XDI specfications). =markus and =drummond would
come from different "roots", since different XDI endpoints are
authoritative for them.
- We talked a bit about equivalence. Giovanni thinks that if there is
a $is statement between two XRIs, then those two XRIs are drawn as
only a single node in the graph. So the node would have two XRIs that
identify it. Markus mentioned that is not how his implementation
currently works.
- A question that follows is how would XDI messaging be affected by
the above. For example, if you have the following XDI graph:
=markus
$is
=markus.sabadello
+name
"Markus Sabadello
=markus.sabadello
+nationality
"AT"
And if you then send this XDI message:
=giovanni
$get
/
=markus
+nationality
Would there be a reply ("AT"), or would there be no reply?
- A similar example would be the effect of a $del message. If
equivalent XRIs are drawn as only a single node in the graph, and you
remove the $is statement via a $del message, would the node then
"split up" into two nodes?
- Giovanni gave a demo of a project his team has been working on
("SMS" - "Simple Mobile Services" - www.ist-sms.org). It allows users
to send small notes about people, locations, services, web sites, etc
from their mobile phone to a server. These notes (so-called MEMs) are
then shared with an online community. It's possible to advertise and
discover new services. Phone security features such as encryption via
the SIM card are used. Various authoring tools are available for
creating new Simple Mobile Services that communicate via MEMs. A web
portal makes it possible to collect and analyze the data that was
collected by the system.
- Giovanni explained that many of his XDI inputs were motivated by use
cases in the SMS system, e.g. XDI Queries.
- We both think it was a good idea to have a chatroom during the last
TC call. We should always use that from now on.
Markus
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