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Subject: Re: [xdi] Minutes: XDI TC Telecon Thursday 1-2PM PT 2010-02-04
Dear Drummond, all, During next call I'd like to illustrate a set of slides which summarizes the assumptions I made for a semantic model for XDI and how they address the issues encountered during our work in last months. As below reported, these slides are mainly intended as a support for writing a technical paper on semantic aspects in XDI, but hopefully parts of its content could then be used to complement the working draft. If someone of you likes to become a coauthor, please let me know. Estimated time for the completition of the paper is two-three months since now. In any case, I will thank the TC in an acknowledgement at the end of the article. Best Regards, Giovanni Def. Quota "Drummond Reed" <drummond.reed@xdi.org>: > Federal Identity, Credentialing, and Access Management TFPAP, Version 1.0.1, > September 4, 2009 > > Following are the minutes of the unofficial telecon of the XDI TC at: > > > Date: Thursday, 04 February 2010 USA > Time: 1:00PM - 2:00PM Pacific Time (21:00-22:00 UTC) > > ATTENDING > > > > Giovanni Bartolomeo > > Markus Sabadello > > Drummond Reed > > > 1) XDI RDF METAGRAPH MODEL & ALTERNATE METAMODELS > > On last week’s telecon, Giovanni said that he would like to propose an > alternative XDI metamodel. While Drummond supports the research into this, > he has concerns about the TC pursuing more than one metamodel for the XDI > 1.0 specification suite, given that with the current metamodel we are very > close to finally producing the first formal XDI 1.0 specifications, and that > several real world implementations badly need these specifications > formalized. > > > > The discussion began with Giovanni asking if the goal was to publish the 1.0 > specifications while semantic issues still remained. Drummond clarified that > he was talking about at least pushing forward to the Working Draft level of > specification, because the TC has taken so long (6 years) just to reach that > point. > > > > There was a short discussion of the timing to move to Working Draft 01. > Drummond said that if he is going to be the editor, he can’t do it until > after the RSA Security conference the first week of March. This would give > us about a month to close issues. > > > > Drummond clarified that he certainly does not want to build any logical > inconsistencies into XDI 1.0. Giovanni explained that his motivation for > proposing a different metamodel is to define formal semantics for the XDI > metamodel that help make sure logical inconsistencies are avoided. The > proposal he is developing are based on the same requirements as the current > metagraph model but makes some different assumptions, thus resulting in > different semantics. > > > > Giovanni suggests that he would like to author a paper about the XDI > metamodel in order to: a) raise the visibility of the work, and b) receive > the feedback of the scientific and academic community on the metamodel and > formal semantics. > > > > Markus observed that he has been working with implementations of the current > metagraph model for over a year now and not experienced any problems, so he > wondered how much value that proof of semantic correctness will add. > Drummond said he pictured Markus’ question as asking about two levels: a > syntactic level (“graph correctness”) and a semantic level (“logical > correctness”). Consistency/correctness at the syntactic/graph level is > necessary but not sufficient for consistency/correctness at the > semantic/logic level. > > > > However Drummond said he believes that the metagraph model will prove to be > logically consistent and correct at both levels. So he is eager to continue > to explore any issues of semantic correctness. > > > > He cited the next topic as an example, so the focus moved to that. > > > > 2) $HAS SEMANTICS CONTINUED > > > > Drummond said that part of the power of the metagraph model is that when > used very precisely, it suggests novel solutions to challenges we have faced > at modeling in XDI certain common constructs in natural language. He sent an > example to the list just before the call: > > > > http://lists.oasis-open.org/archives/xdi/201002/msg00003.html > > > > He reviewed the message with Giovanni and Markus to go over how a precise > application of the metagraph predicate $, which identifies the current > context, can be used to express both possession and plurality of XDI RDF > subjects. Due to the coincidence that the $ global context symbol was chosen > to represent this resource, what is truly stunning is how much the resulting > XDI expression ends out reading like the same natural language expressions > in English. > > > > POSSESSIVE > > =bill/$has/$ <==> (=bill/$) > <==> =bill$ > > =bill$/$has/+car <==> (=bill$/+car) > <==> =bill$+car > > > > PLURAL > > +car/$has/$ <==> (+car/$) > <==> +car$ > > > > POSSESSIVE + PLURAL > > =bill$/$has/+car$ <==> (=bill$/+car$) > <==> =bill$+car$ > > > > Both Markus and Giovanni laughed as hard as Drummond did when they first saw > this result. > > > > Markus then asked how one would render an English expression like “the car’s > windshield”. Drummond pointed out that there is a significant difference > between “the car’s windshield” and “car’s windshield”. The latter identifies > a specific class of windshield. The former identifies one instance of that > class by adding the definitive > article<http://en.wikipedia.org/wiki/Article_%28grammar%29#Definite_article>“the”. > > > > Giovanni said he has had the same issue of identifying an instance of an > object that is not a person or an organization. > > > > Drummond said this same issue had come up in his consideration of the > English language expressions above. Ironically, the solution appears to once > again to involve the key XDI concept of context. The definitive article > “the” expresses that the subject being referenced is known in the current > context, or more precisely, “is uniquely distinguished in the current > context”. In that case, since $ represents the current context in the > current XDI RDF metagraph model, and since all XDI subjects within that > context are uniquely XRI-addressable, this means the XDI equivalent of the > English phrase “the car” would be: > > > > $+car > > > > The literal translation would be “the XDI RDF subject +car in the current > context”. Note that this identifies a different XDI RDF graph than +car by > itself, because +car by itself identifies the generic class of “car”, and > not any specific car. > > > > $+car is definitive since $ represents the current context, of which there > can be only one. This means the way to express an indefinite > article<http://en.wikipedia.org/wiki/Article_%28grammar%29#Indefinite_article>such > as “a car” would be to make it explicit that the context being > referenced could be any context. That can be done with a cross-reference, > which is always relative to the XRI that it follows. So, the XDI equivalent > of the English phrase “a car” would be: > > > > $(+car) > > > > > > 3) NEXT CALL > > > > The next call is next week at the regular time. Drummond noted that due to > work commitments leading up to RSA Conference the first week of March, he > may have to miss several calls after next week’s call. > ---------------------------------------------------------------- This message was sent using IMP, the Internet Messaging Program.
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