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Subject: golden triangle (was Re: [xdi] $is is the universal inverserestriction)
-1. I'd like "predicate" better, to maintain backward compatibility with RDF. BTW there are currently many issues with the "golden triangle" which are still very obscure (at least to me), including: $is$a as $word relating predicates with objects, $is and self referencing arc definition, $has$a definition as traversal of subject and predicate, +x/+y/+y and +x/+y/+x+y reintroduced, after we agreed that they were not needed, etc... Note that the current specs are totally based on the golden triangle: http://wiki.oasis-open.org/xdi/XdiOne/AddressingAndGraphModel This way it becomes very difficult - or sometimes even impossible - to think at XDI productions in terms of description logic. I think it would be better to rediscuss together the golden triangle, and probably revise the current specs page accordingly. Kind Regards, Giovanni Def. Quota "Drummond Reed" <drummond.reed@xdi.org>: > I don't think it's any more confusing than "predicate". "verb" is just a > role - the same XRI could be a subject, verb, and object (especially in an > XDI dictionary). > > But that's just one person's view. What do others think? > > =Drummond > > On Thu, Jun 10, 2010 at 2:28 AM, Markus Sabadello > <markus.sabadello@xdi.org>wrote: > >> Oh nooo I'll have to rename lots of stuff in XDI4j :) >> >> But seriously, isn't "verb" a bit confusing? +name, +address etc. don't >> look like verbs to me. >> >> Markus >> >> >> On Thu, Jun 10, 2010 at 10:49 AM, Drummond Reed >> <drummond.reed@xdi.org>wrote: >> >>> >>> >>> On Thu, Jun 10, 2010 at 12:51 AM, Joseph Boyle >>> <boyle.joseph@gmail.com>wrote: >>> >>>> >>>> On Jun 9, 2010, at 11:22 PM, Drummond Reed wrote: >>>> >>>> Joseph, first, my apologies for not replying earlier - I had another trip >>>> this week so my email is way behind. >>>> >>>> But we have another XDI TC telecon coming up tomorrow so I wanted to move >>>> discussion forward on the individual issues/questions about the example >>>> PDX document <http://wiki.oasis-open.org/xdi/PdxExample>. Here are my >>>> answers to your two questions about $is (copied from below to keep the >>>> thread clean): >>>> >>>> > 1) How do the two roles of $is form a single coherent concept? Right >>>> now the modifier role (as a passive voice marker modifying the following >>>> verb) and the standalone role (as the copulative verb) seem like distinct >>>> definitions to me. I realize this is analogous to the English verb "to be" >>>> that also serves in both these roles, but is there a philosophical / >>>> semantic / formal (take your pick) argument that this should logically be >>>> the case in XDI? >>>> >>>> You phrase that question very well. I have been thinking that in the >>>> spec, we need to define the semantics for each of the metagraph predicates >>>> for each of the following uses: >>>> >>>> 1) Standalone, e.g., $is >>>> >>>> 2) As a restriction on another predicate (i.e., preceeding it, e.g., >>>> $is+foo) >>>> >>>> 3) As an extension on another predicate (i.e., following it, e.g., >>>> +foo$is) >>>> >>>> >>>> Agreed, we must do this, and explain what the 3 usages for a given >>>> predicate have in common. (Are these the only 3, or are there even more >>>> possible uses?) >>>> >>> >>> I left out the other six options: Using the metagraph predicate as a 1) >>> standalone subject, 2) subject restriction, or 3) subject >>> extension, as well >>> as a 4) standalone object, 5) object restriction, 6) object extension. >>> >>> For many of those, the answer may be "undefined", but for some there are >>> very good answers. For example, $ as a standalone subject is the >>> XDI context >>> self-descriptor; and $has and $a are both used as the proposed subject >>> extensions to create link contracts as shown in the lower part of >>> the example >>> PDX document <http://wiki.oasis-open.org/xdi/PdxExample>. >>> >>>> >>>> I believe the definitions in each of these three roles must be logically >>>> consistent. For example, the definition of $is as a standalone >>>> predicate is >>>> synonymity between the subject XRI and object XRI (they both identify the >>>> same logical resource). This is as shown as a >>>> reflexive<http://en.wikipedia.org/wiki/Reflexive_relation>arc >>>> (self-referential -- originating and terminating in the same >>>> node) as >>>> illustrated in the golden >>>> triangle<http://www.oasis-open.org/committees/download.php/37568/xdi-golden-triangle.png>. >>>> >>>> >>>> >>>> The Golden Triangle diagram (I'm tempted to say the XDI Holy Trinity but >>>> should probably refrain) itself shows S and O as separate nodes though >>>> connected by arrows labeled $is. For the arc to be reflexive, S >>>> and O would >>>> have to merge and become a single node. Sorry if this sounds too >>>> literal. We >>>> do understand "$is" as making S and O equivalent - but this is something >>>> that we have to explain with text external to the diagram. Looking at the >>>> diagram alone naively, it is not obvious that the $is arcs merge >>>> S and O but >>>> that the other $a, $has arcs do not make S and P equivalent or P and O >>>> equivalent. >>>> >>> >>> I agree that the Golden Triangle diagram by itself does not make it clear >>> that the $is arc is reflexive. It needs some text with it to >>> explain that. I >>> have a separate intermediate diagram that explains the origins of >>> the Golden >>> Triangle diagram that makes that much clearer. I propose we use both in the >>> final spec. >>> >>>> >>>> The definition of $is as a restriction on another predicate is that it >>>> expresses the inverse of that predicate, e.g., the inverse of +b is $is+b >>>> (example: +a/+b/+c <=> +c/$is+b/+a). The logical connection with $is as a >>>> standalone verb is that $is, being reflexive arc, is being used >>>> to describe >>>> the verb it is restricting. As a reflexive arc, it is literally >>>> "reversing" >>>> the restricted verb. So $is+foo is the reverse (inverse) of +foo. >>>> >>>> This is one simplest yet most powerful examples of the utility of >>>> semantic (non-opaque) identifiers in XDI. >>>> >>>> >>>> > 2) One difference I notice between XDI terminology and linguistics >>>> terminology is that in the latter, "predicate" means verb together with >>>> object, not simply the verb. >>>> >>>> Ahhh, I didn't know that. As you know, I have no formal background in >>>> either linguistics or formal logic, so I am constantly learning >>>> nuances like >>>> this. What's the solution: are you suggesting we use the term >>>> "verb" instead >>>> of "predicate"? As in: XDI subject, XDI verb, XDI object? >>>> >>>> >>>> http://en.wikipedia.org/wiki/Predicate lists the differing meanings in >>>> grammar, logic, etc. >>>> >>>> XDI gets the term "predicate" from RDF which gets it from mathematical >>>> logic, where it specifically means a boolean-valued function. In this case >>>> both S and O would be considered arguments to the predicate, and >>>> the boolean >>>> result True from P(S,O) is expressed by the fact that the >>>> predicate is being >>>> stated / graphed at all while the boolean result False from >>>> P(S,O) would be >>>> expressed by not stating / graphing anything. This makes sense in >>>> one sense, >>>> but may not be the most intuitively obvious meaning, in addition to the >>>> conflict with the natural-language grammar that most people are familiar >>>> with. >>>> >>>> I would vote for "verb" not "predicate" in line with the trend towards >>>> using simple everyday natural-language-like terms in XDI, which >>>> has included >>>> using "$is", "$has", "$a" to replace more technical terms. This would be >>>> another break with RDF terminology, which may be good or bad depending on >>>> your viewpoint. I think some other knowledge representation systems have >>>> used "verb" in some way, but don't remember specifically. >>>> However, the only >>>> programming language I can think of offhand where "verb" is part of normal >>>> terminology is COBOL. :/ >>>> >>> >>> I agree with your logic, and with using "subject, verb, object" instead of >>> "subject, predicate, object". If anyone on the TC disagrees, please post, >>> else I will start using that in all the XDI-related text I'm writing. >>> >>> Thanks, >>> >>> =Drummond >>> >>> >>> >> > ---------------------------------------------------------------- Invito da parte dell'Ateneo: Il tuo futuro e quello della Ricerca Scientifica hanno bisogno del tuo aiuto. Dona il 5 x mille all'Universita' di Roma Tor Vergata codice fiscale: 80213750583 http://5x1000.uniroma2.it
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