- From: Richard Cyganiak <richard@cyganiak.de>
- Date: Tue, 11 Sep 2012 18:46:13 +0100
- To: Antoine Zimmermann <antoine.zimmermann@emse.fr>
- Cc: public-rdf-wg@w3.org
On 11 Sep 2012, at 14:37, Antoine Zimmermann wrote: > Follow-up of my two previous emails: > > > 4.1. owl:imports entailment. > > Good. Minor suggested change: > > "If <r1,r2> in IEXT(I(owl:imports)) and IGEXT(r2) is defined then IGEXT(r1) entails IGEXT(r2)." > > --> > > "If <r1,r2> in IEXT(Id(owl:imports)), IGEXT(r1) and IGEXT(r2) are defined then IGEXT(r1) E-entails IGEXT(r2)." Fixed. > Remark: if we opt for IRI-IGEXT, then the definition becomes: > > "If <Id(n1),Id(n2)> in IEXT(Id(owl:imports)), IGEXT(n1) and IGEXT(n2) are defined then IGEXT(n1) E-entails IGEXT(n2)." > > > > > 4.2. Web entailment. > > "If r is a web resource with at least one representation in an RDF format" > > this condition cannot be checked by a reasoner. You need an oracle that tells you when an IRI denotes a web resource. Just dereference it. > This oracle may be something like httpRange14 or simply a dereferencing function + reasoning to detect identity. > > This means that there must be one more step of indirection, which you do not have if you use IRI-IGEXT. With IRI-IGEXT, Web entailment associates with an IRI whatever RDF graph you get by dereferencing the IRI. *shrug*. I don't see the difference. <snip httpRange-14/owl:sameAs argument> > That's why I prefer IRI-IGEXT. The resource denoted by dbpedia:Tim_Berners-Lee does not have a representation because it does not return a 200 or 301 or 302. With the notion of web-entailment that I defined in the page, there would be no graph of that name. There would be one at <http://dbpedia.org/data/Tim_Berners-Lee>. If you define web-entailment differently then you may get different results, but a debate about the pros and cons of different ways of defining this web-entailment seems like a distraction at this point. I don't wish to get into an httpRange-14 debate. > 4.3. Direct graph semantics. > > I don't think this is going to fly. Not sure what you mean by “fly”. It shows an example and use case for extending the semantics. It's not a proposal for standardization. > It is way too restrictive. Not sure how it is restrictive. It says that by typing something as rdf:Graph, you can actually make it denote the graph given in a <name,graph> pair. This doesn't seem restrictive to me. > I believe that what we need is a flexible vocabulary à la Service description. Such a vocabulary should not clutter RDF reasoners with strong semantics constraints. I'm not sure how SPARQL Service Description is more flexible than the single term rdf:Graph, or why such flexibility is desirable, or why you consider a semantic extension presented as an example for a possible extension “clutter”, or what's so strong about the semantic constraints in that extension. > However, people who are interested in implementing support for the vocabulary can interpret the terms in a special way. People already do that. There are tools that display instances of foaf:Person in a special way. There are Web crawlers that interpret the voiD vocabulary in a special way. They do not need that the special interpretation be hard coded in reasoners. I don't know what your point is. A semantic extension is not a requirement for hard coding anything in a reasoner. > If I had to directly talk about a graph in a named graph, I would do it like this: > > :g a sd:Graph; > :validityTime "1998-09-11"^^xsd:date; > ... > :g { :bob :employedBy :ibm } > > It works, as long as I am using an agreed upon, explicit specification of a shared conceptualisation, a.k.a. an ontology. Yeah, and that's exactly the example I gave, except I called it rdf:Graph instead of sd:Graph, and formalized the implicit assumption that :g actually denotes { :bob :employedBy :ibm } as opposed to some other graph. You can't do that just by defining an ontology. The benefit of formalizing this is that, for example, if I define a Turtle datatype then it will just work, and I can infer { :g owl:sameAs ":bob :employedBy :ibm"^^xxx:Turtle } from the dataset above, modulo namespace declaration. Best, Richard > > > AZ. > > > > > Le 11/09/2012 11:46, Richard Cyganiak a écrit : >> On 10 Sep 2012, at 17:30, Richard Cyganiak wrote: >>> Two other things that I'd quite like to see before we can call the proposal complete: >>> >>> 1. Some thinking on how it addresses our graph use cases. (Do we have an “official” list of those? I've lost track with all the various documents.) >>> >>> 2. Some examples for semantic extensions, in order to show that various other proposed semantics can actually be done as proper semantic extensions of this minimal dataset semantics. >> >> I've worked a bit on this item and made attempts to formalize three semantic extensions: >> >> * owl:imports (formally explains how owl:imports works in RDF datasets) >> * web datasets (formally defines that stuff published on the web is asserted) >> * direct graph semantics (permits "literal" immutable graphs) >> >> http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/Minimal-dataset-semantics#Possible_Semantic_Extensions >> >> I'm not proposing that we should standardize any of this; the intention is merely to explore how flexible/extensible the semantics proposed on that page is. >> >> Again, I'm not really good at this formal semantics stuff, so this might all be spectacularly wrong. >> >> Best, >> Richard >> > > -- > 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/ >
Received on Tuesday, 11 September 2012 17:46:45 UTC