On Mar 27, 2013, at 8:37 AM, David Booth wrote: > Hi Oliver, > > On 03/25/2013 04:02 PM, Oliver Ruebenacker wrote: >> Hello David, >> >> We agree that there are different interpretations. But you haven't >> shown that the boundaries between interpretations are graphs >> boundaries (others, including me, think that each interpretation is >> global). > > I don't know what you mean by "boundaries between interpretations". > An interpretation may be applied to any graph or statement to determine its > truth value (or to a URI to determine the resource to which it is bound in > that interpretation). > > The notion of a graph boundary is purely a matter of convenience and utility. > A graph can consist of *any* set of RDF triples. If you wanted, you could > apply an interpretation to a graph consisting of three randomly selected > triples from each RDF document on the web, but it probably wouldn't be very > useful to do so, because you probably would not care about the truth value of > that graph. We generally only apply an interpretation to a graph whose truth > value we care about. > > An interpretation corresponds to the *use* of a graph. Suppose I have a > graph that "ambiguously" uses the same URI to denote both a toucan and its > web page, without asserting that toucans cannot be web pages: > > @prefix : <http://example/> > :tweety a :Toucan . > :tweety a :WebPage . > > When a conforming RDF application takes that RDF graph as input, assumes it > is true, and produces some output such as "Tweety is a toucan", in effect the > application has chosen a particular interpretation to apply to that graph. > In effect, the choice of interpretation causes the app to produce that > particular output. For example, the app might categorize animals into > species, choosing an interpretation that maps :tweety to a kind of bird. But > a different conforming RDF application that only cares about web page > authorship might take that *same* RDF graph as input and choose a different > interpretation that maps :tweety to a web page, instead outputting "Tweety is > a web page". In effect, the app has chosen an interpretation that is > appropriate for its purpose. > > If the graph had also asserted :Toucan owl:disjointWith :WebPage, then the > graph cannot be true under OWL semantics, and the graph (as is) would be > unusable to both apps. > >> >> That makes me wonder whether you consider it in conformance with the >> specs to choose different boundaries? >> >> For example, would you consider it conforming to apply a different >> interpretation to each statement? Or how about a different >> interpretation for each node of a statement? Do you see anything in >> the specs against doing so? > > Sure it is in conformance with the spec. An interpretation can be applied to > any graph or any RDF statement. And certainly you could determine the truth > value of N different statements according to N different interpretations. > But would it be useful to do so? Probably not. Furthermore, if two > statements are true under two different interpretations, that would not tell > you whether a graph consisting of those two statements would be true under a > single interpretation. > > OTOH, it *is* useful to apply different intepretations to different graphs, > and one reason is that you may be using those graphs for different > applications, each app in effect applying its own interpretation. But the > fact that those graphs may be true under different interpretations does *not* > tell you whether the merge of those graphs will be true under a single > interpretation. > > The RDF Semantics spec only tells you how to compute the truth value of one > <interpretation, graph> pair at a time, but you can certainly apply it to as > many <interpretation, graph> pairs as you want -- in full conformance with > the intent of the spec.
Not with the *intent*, even if I have to concede that it does conform to the letter. The intention of the spec is to describe a model-theoretic semantics for RDF and RDF extensions. What you are doing, David, is not model theory semantics and does not describe any useful notion of interpretation. Pat > This is the same as if I define a function f of two arguments, such that > f(x,y) = x+y, that function definition only tells you how to compute f(x,y) > for one pair of numbers at a time, but you can certainly apply it to as many > pairs as you want, without in any way violating the intent of f's definition. > > David > > ------------------------------------------------------------ IHMC (850)434 8903 or (650)494 3973 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 mobile phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
