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Subject: Re: [xdi] notes from meeting in Nice, Jan 29 2009
Thank you, useful to get that level of explicitness. I just discovered today reviewing the RDF model that = is itself an XRI for the = registry, so that =drummond => =/$has/drummond : your model addresses this nicely. You're not making any commitment about what the relationship is between +x+y and +y. I had been suggesting +x+y/$is$a/+y, but after revisiting the RDF model (and statements such as $get$a$xsd$boolean), I'm not as confident about that, so you needn't change anything. The model does not relate $has to $has$a. I think there is clearly such a relation --- the object of $has is the unique, possibly aggregate value, the object of $has$a includes those values in classes --- and it would be nice to have a diagram showing the relation between =abraham/$has$a/+son and =abraham/$has/=isaac. The relationship of $is and $is$a, on the other hand, was always somewhat murky, and it would not be useful to attempt to illustrate it. In the new dispensation, the inverting word is $is, not $a. :-) On 30/01/2009, at 13:15, Markus Sabadello wrote: > Hi Giovanni (and others), > > I'm trying to summarize in a few words what we talked about. Please > correct me if I made a mistake or forgot anything. > > - We had a look at the xdi-rdf-global-graph-proposal-v1 which > Giovanni posted about a week ago: > http://www.oasis-open.org/committees/download.php/30802/xdi-rdf-global-graph-proposal-v1.pdf > > - The basic graph model described in that document is essentially > the same as the one we are all familiar with (i.e. subject/predicate/ > object triples), but the document proposes a new methodology for > drawing the graph. The main innovation is to draw EVERYTHING that > has an XRI as a node (including predicates!). Arcs are drawn between > the nodes, but arcs themselves don't have XRIs. A typical statement > consisting of subject, predicate and object would be drawn as three > nodes and three arcs. > > - Arcs are colored to indicate which statement they belong to. > > - A node with a given XRI never appears twice in the graph, but it > can of course be part of more than one statement. For example if you > have the following two statements: > =markus/+email/'markus.sabadello@gmail.com' > +email/$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 > (*)(*)(*) http://www.opoudjis.net DR NICK NICHOLAS; LINK AFFILIATES, MELBOURNE skype:opoudjis opoudjis@optushome.com.au "Some of the English might say that the Irish orthography is very Irish. Personally, I have a lot of respect for a people who can create something so grotesque." -- Andrew Rosta
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