- From: Ivan Herman <ivan@w3.org>
- Date: Thu, 23 Aug 2012 17:02:35 +0200
- To: Antoine Zimmermann <antoine.zimmermann@emse.fr>
- Cc: public-rdf-wg@w3.org
On Aug 23, 2012, at 16:20 , Antoine Zimmermann wrote: > Ivan, > > > Le 23/08/2012 15:11, Ivan Herman a écrit : >> Hi Antoine, >> >> (Sorry, this mail is a little bit long. tl;dr: I actually like the >> direction of where this is going:-) > > I'm glad and relieved to read that :) Wait, I am only one among many... [skip] > > >> >> 2nd piece >> >> What Richard has defined a while ago in [2] for datasets is, > > I think you used the wrong URL for [2]. Richard did this: > > http://www.w3.org/2011/rdf-wg/wiki/Yet_Another_Dataset_Proposal > Oops, sorry (to Richard? to you? :-) Anyway, I of course meant the document I referred to. Ie, the one you edited. [snip] > > >> This means that, in theory, the >> application/data provider can choose the combination of entailment >> regimes per graphs: G1 would be considered for OWL-RL, whereas Gk is >> subject to RIF, for example. >> >> As a base line, ie, if no other information is known, then the >> No-Semantics is the entailment regime used for all the G1,G2,...,Gk >> graphs. (Does this also apply to the default graph?) > > If it is not applied to the default graph, then what semantics apply to it? > My instinct would say that, by default, Simple Entailment would apply to the Default Graph; that would be, I believe, the reflection of quoting. [snip] > > >> _Personally_, I like where this is going, although I am not sure it >> would cover all the use cases we had in the past. For example, one of >> the use case that did come up is what we used to call 'merge >> semantics', meaning that all inferences and constraints checks are >> made on the merge of all the graphs (including the default graph). >> This is not covered by this structure but, maybe, this is not >> important. > > Yes, it does not cover the merge/union semantics. But they are simple semantic extensions, for which we can provide (or a future WG) vocabulary to specify. > would that be a semantic extension of the scheme you propose, or something totally orthogonal to it? I do not see how it fits in your scheme; that one does not speak about the merging of the particular graphs... > >> (I am also a little bit worried about the complexity for users. We >> shall see the feedbacks.) > > The formal semantics will certainly look quite complex, but it can be explained in a rather simple way. In a nutshell, it says that: > > "All RDF graphs in an RDF dataset don't mean the same thing. To be explicit about what they mean, we provide a vocabulary that specify the semantics of each graph. We call the semantics assigned to a <name,graph> pair its entailment regime, because it determines what entailments are valid for that pair. For example ..." > > Then we have to warn the people who would like to read the formal details should be well armed. > :-) Sounds familiar... > >> >> Also, some technical issues/questions: >> >> 1. (I should have looked at that yesterday, sorry.) I found the >> terminology used in [2] a bit confusing and I have the feeling that >> there is an overload of the letter 'E'... At present, it says >> >> [[[ Moreover, dataset interpretations are defined with respect to an >> entailment regime E, as defined in SPARQL 1.1 Entailment Regimes. Let >> KE be the set of all E-interpretations. The interpretation of an RDF >> Dataset (G, (<n1>,Gn1), ..., (<nk>,Gnk)) over vocabulary V is a pair >> (I,Con) where I is an E-interpretation of G (the default graph) and >> Con is a mapping from V to KE. >> >> A dataset-interpretation (I,Con) of a vocabulary V wrt entailment >> regime E satisfies an RDF Dataset (G, (<n1>,Gn1), ..., (<nk>,Gnk)) >> iff I E-satisfies G, and for all i in [1..k], Con(ni) exists and >> E-satisfies Gni. ]]] >> >> I *could* read this sentence as asking that *all* constituent graphs, >> including the default graph, must use the same interpretation. Isn't >> it: > > Yes, that was the idea when I wrote it. The idea of having distinct regimes for distinct <name,graph> pairs only made sense to me when I drafted the new proposal yesterday. > > This is why I marked the following in the new proposal: > > "TODO: modify the semantics such that different entailment regimes can be used for different named graphs." > > Oops, sorry, I missed that. >> [[[ Moreover, dataset interpretations are defined with respect to an >> entailment regime E, as defined in SPARQL 1.1 Entailment Regimes. Let >> KE be the set of all interpretations as defined in SPARQL 1.1 plus >> the No-Semantics. The interpretation of an RDF Dataset (G, >> (<n1>,Gn1), ..., (<nk>,Gnk)) over vocabulary V is a pair (I,Con) >> where I is an E-interpretation of G (the default graph), and Con is a >> mapping from V to KE. >> >> A dataset-interpretation (I,Con) of a vocabulary V wrt entailment >> regime E-satisfies an RDF Dataset (G, (<n1>,Gn1), ..., (<nk>,Gnk)) >> iff I E-satisfies G, and for all i in [1..k], Con(ni) exists and >> Con(ni)-satisfies Gni. ]]] >> >> (Note that last 'Con(ni)-satisfies Gni'.) > > Con(ni) assigns a term of the vocabulary to an E-interpretation. It does not assign a term to an entailment regime. This is something I have to think about, but I have an idea. It's not trivial, as far as I can see. > I am not sure I understand. Why can't Con(ni) directly assign a term to an entailment regime? As far as I can see, that is the only place it is used, so we can define it as we wish... > >> Terminologically and in line with the outline you had, I actually >> o.k. to call that an 'E-interpretation of the dataset'; after all, >> each entailment regime is parametrized, wether it applies to the >> default graph or not. >> >> 2. If I choose to use, say, OWL as an entailment regime for Gi, how >> do I specify *which* OWL Ontology should be used for that purpose? I >> know this is also a question one may about current graphs, too, but >> the situation becomes a bit more complex if we have many different >> graphs. Would we require some sort of a follow-your-nose on the terms >> used in Gi and allow the system to find the relevant ontologies? Or >> would we suppose that, at least conceptually, Gi has all the >> ontologies as part of the graph already, and we decide that this is >> not our problem? > > Entailment regimes are special semantic conditions that are hard coded in consensual standards. We don't define an entailment regime per-ontology. Right. > If you want the knowledge of the ontology to influence the inference on a named graph, then you can put the ontology inside the graph. Yes, that is one of the options I raised. And, conceptually, that can work, this is how the current SW works, after all: the ontology used for entailment of a particular graph is really 'paired' out of band. My only worry is that, in practice, if we have datasets with very different entailment regimes, this may become very complicated for a deployment, unless we provide some standard (though probably optional) ways to do it. > But I understand that it would be more convinient to be able to refer to an external document (whether it is OWL or plain RDF). Something like an "import". Truely useful but I doubt we should take care of this in this WG. Let us leave some work to do for the future generations :) > I would not close the door on that if this whole semantic line is going in a satisfactory direction. > >> For RIF, SPARQL/RIF introduced the rif:usedWithProfile. Maybe >> something similar, but also for OWL, should be added to those >> parameters that you defined. > > Maybe. Let us see first how people react to this proposal. > Sure. There may be huge semantic pitfalls that I certainly cannot foresee, I would never claim to have an expertise in the semantic side of things. One issue I see but I cannot properly formulate is the question whether, in an (ni,Gi) pair, we can or we cannot really rely that the 'ni' really really behaves like a URI which uniquely identifies a Graph. Isn't it possible that two different applications may reuse 'ni' to signify two different graphs. 'Cause if so, then the entailment statements (which are RDF statements somewhere in the wild) will, theoretically, lead to problems. But maybe this is one of those things we will have to live with. > >> 3. My other issue is a question. The No-semantics means that there >> are no semantic conditions on the graphs. However, looking at first >> table of semantic conditions in section 1.4 of the RDF Semantics >> document, although that section says 'denotation of ground graphs', >> the first four condition is not dependent at all on blank nodes, it >> just defines a bit what a graph structure is. > > Seems possible too. I guess it does not matter that much, as the no-semantics has only one trivial entailment: all graphs entail themselves and only themselves. > As I said, it is not very important, but the role of these semantic conditions, at least for me, is also to restrict what can be a model at all and, through that, describe some sort of a constraints on how the data can be organized if it is truly RDF. Cheers Ivan >> I believe that can be >> safely added to the No-semantics as a semantic condition. I *think* I >> understand why the other two are not added as conditions: we do not >> want to get into the blank node store at this point. >> >> Whether we expand the no-semantics with those or not is not *really* >> important, though; I just wanted to understand why those were left >> out. >> >> Thanks >> >> Ivan >> >> >> [1] >> http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/Dataset-semantics-2.0 >> [2] http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/Dataset-semantics >> >> >> On Aug 22, 2012, at 16:57 , Antoine Zimmermann wrote: >> >>> So, I made a new wiki page in a tentative to reconciliate the >>> different semantics. >>> >>> http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/Dataset-semantics-2.0 >>> >>> Basically, I define a super-weak semantics of RDF graph, which can >>> be used as an underlying entailment regime for the dataset >>> semantics of [1]. >>> >>> Then, I put an example of a possible vocabulary to allow more >>> expressiveness. The vocabulary is mirroring some of the terms of >>> SPARQL 1.1 service descriptions [2]. >>> >>> This truly makes the "base" semantics very very weak but allows one >>> to extend it to any variant on top of it. >>> >>> >>> [1] http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/Dataset-semantics >>> [2] >>> http://www.w3.org/TR/2009/WD-sparql11-service-description-20091022/ >>> >>> >>> >>> > AZ >>> >>> Le 22/08/2012 16:33, Ivan Herman a écrit : >>>> >>>> On Aug 22, 2012, at 15:54 , Pat Hayes wrote: >>>> >>>>> >>>>> On Aug 22, 2012, at 2:04 AM, Ivan Herman wrote: >>>>> >>>>>> >>>>>> On Aug 21, 2012, at 21:48 , Pat Hayes wrote: [snip] >>>>>>>> >>>>>>>> >>>>>>>> Antoine, I have the impression that we are actually in >>>>>>>> agreement. The document we have put forward has two >>>>>>>> essential points: >>>>>>>> >>>>>>>> - we would have a default semantics in the form of the >>>>>>>> quoting semantics >>>>>>> >>>>>>> >>>>>>> Whoa. I do not know what y'all mean by a "default >>>>>>> semantics". Is this a default that can be overridden? If >>>>>>> so, I know of NO semantic theory anywhere in logic or >>>>>>> linguistics that can provide this. If y'all want this, you >>>>>>> are on your own. >>>>>>> >>>>>>> If not, what exactly is it supposed to mean? >>>>>>> >>>>>>> Pat >>>>>> >>>>>> >>>>>> What I meant is: this is the semantics that is standardized >>>>>> to be valid in the absence of any other indication. I did not >>>>>> say anything else. >>>>> >>>>> And Antoine agrees. OK, then a better term would be "weak" or >>>>> "minimal" semantics. "default" sounds like nomonotonicity >>>>> (being overridable) to me. >>>> >>>> Agreed, sorry for my sloppiness. 'Minimal' sounds indeed good to >>>> me. >>>> >>>> Ivan >>>> >>>> >>>>> >>>>> Pat >>>>> >>>>>> >>>>>> Ivan >>>>>> >>>>>> >>>>>> ---- Ivan Herman, W3C Semantic Web Activity Lead Home: >>>>>> http://www.w3.org/People/Ivan/ mobile: +31-641044153 FOAF: >>>>>> http://www.ivan-herman.net/foaf.rdf >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>> >>>>> ------------------------------------------------------------ >>>>> 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 >>>>> >>>>> >>>>> >>>>> >>>>> >>>> >>>> >>>> ---- Ivan Herman, W3C Semantic Web Activity Lead Home: >>>> http://www.w3.org/People/Ivan/ mobile: +31-641044153 FOAF: >>>> http://www.ivan-herman.net/foaf.rdf >>>> >>>> >>>> >>>> >>>> >>>> >>> >>> -- Antoine Zimmermann ISCOD / LSTI - Institut Henri Fayol École >>> Nationale Supérieure des Mines de Saint-Étienne 158 cours Fauriel >>> 42023 Saint-Étienne Cedex 2 France Tél:+33(0)4 77 42 66 03 >>> Fax:+33(0)4 77 42 66 66 http://zimmer.aprilfoolsreview.com/ >>> >> >> >> ---- Ivan Herman, W3C Semantic Web Activity Lead Home: >> http://www.w3.org/People/Ivan/ mobile: +31-641044153 FOAF: >> http://www.ivan-herman.net/foaf.rdf >> >> >> >> >> >> >> > > -- > Antoine Zimmermann > ISCOD / LSTI - Institut Henri Fayol > École Nationale Supérieure des Mines de Saint-Étienne > 158 cours Fauriel > 42023 Saint-Étienne Cedex 2 > France > Tél:+33(0)4 77 42 66 03 > Fax:+33(0)4 77 42 66 66 > http://zimmer.aprilfoolsreview.com/ > ---- Ivan Herman, W3C Semantic Web Activity Lead Home: http://www.w3.org/People/Ivan/ mobile: +31-641044153 FOAF: http://www.ivan-herman.net/foaf.rdf
Received on Thursday, 23 August 2012 15:03:09 UTC