- From: Jos de Bruijn <debruijn@inf.unibz.it>
- Date: Tue, 17 Feb 2009 12:21:31 +0100
- To: Axel Polleres <axel.polleres@deri.org>
- CC: Dave Reynolds <der@hplb.hpl.hp.com>, RIF WG <public-rif-wg@w3.org>
- Message-ID: <499A9DBB.5080705@inf.unibz.it>
I tried to implement your wishes. Please check whether the current text is okay for you: http://www.w3.org/2005/rules/wiki/SWC#Importing_RDF_and_OWL_in_RIF Axel Polleres wrote: > > Dave Reynolds wrote: >> The OWL (1) specs are not entirely internally consistent in this >> regard as you've jointly pointed out. >> >> In current practice many applications and tools deal with ontologies >> (and datasets in the case of SPARQL) not published at their URI, while >> recommended good practice is to publish there. >> >> My preference would be: >> >> - use Axel's suggested phrasing of "referred to by u1,...,un" >> >> - say that recommended good practice is to resolve this reference by >> treating the URI as a web location but that implementations MAY >> support other mechanisms (e.g. local caches) > > +1 > >> - leave behaviour in the case where the reference cannot be resolved >> undefined (in practice any tool would report such a failure but there >> are use cases where proceeding with the subset of data you have >> available at present is preferable to a complete abort) > > we are actually developing tools which try to be tolerant in this > respect, i.e. issue a warning only, but still proceed in case of e.g. a > 404 for some RDF import. So, indeed I would be either in favor of > leaving this to the implementation or suggesting to treat such graph as > emptyt and getting back a warning rather than prescribe to terminate > with an error. > >>> related: what if pi denotes the OWL DL profile, but ui does not point to >>> an OWL DL ontology? Should the document be rejected? I think so. > > interesting aspect indeed. > >> Seems reasonable so long as the requirement is SHOULD and not MUST. A >> species check is moderately expensive and allowing implementers the >> possibly to omit this in some circumstances would also seem reasonable. >> >> Dave >> >> >> Jos de Bruijn wrote: >>> As a clarification: >>> the OWL2 document you are referring to is merely a "normal" working >>> draft; it is not in last call, and I know for a fact that there have >>> already been substantial (and substantive) changes in the document since >>> the working draft of December. So, this is not something we should base >>> our decisions on. >>> >>> The section from the OWL semantics you are referring to is concerned >>> with the abstract syntax, not with RDF documents on the web. In fact, >>> when going to the RDF world in section 5.4 [1] I read: >>> "[A collection of OWL DL ontologies] O is said to be imports closed iff >>> for any URI, u, in an imports directive in any ontology in O the RDF >>> parsing of the document accessible on the Web at u results in T(K), >>> where K is the ontology in O with name u." >>> >>> This is very much in line with what we wrote in the RDF and OWL >>> compatibility document. >>> >>> all that said, I don't care too much about this issue. But we need to >>> get our facts straight when referring to other specifications. >>> >>> >>> Best, Jos >>> >>> [1] http://www.w3.org/TR/owl-semantics/rdfs.html#5.4 >>> >>> Axel Polleres wrote: >>>> I am a bit surprised to see that we refer to a "RDF graphs accessible >>>> from the locations u1,...,un" in RIF imports, which suggests that we >>>> talk about URLs here, rather than URIs. >>>> >>>> Neither OWL, nor SPARQL, nor OWL2 do this: >>>> >>>> OWL [2, Section 3,4]: >>>> "The imported ontology is the one, if any, that has as name the >>>> argument >>>> of the imports construct. (This treatment of imports is divorced from >>>> Web issues. The intended use of names for OWL ontologies is to make the >>>> name be the location of the ontology on the Web, but this is outside of >>>> this formal treatment.)" >>>> >>>> SPARQL [3, section 8]: >>>> "A SPARQL query is executed against an RDF Dataset which represents a >>>> collection of graphs. An RDF Dataset comprises one graph, the default >>>> graph, which does not have a name, and zero or more named graphs, where >>>> each named graph is identified by an IRI." >>>> >>>> OWL2 [4, Section 9]: >>>> "Definition 3.1 (Import Closure): Let K be a collection of RDF >>>> graphs. K >>>> is imports closed iff for every triple in any element of K of the >>>> form x >>>> owl:imports u then K contains a graph that is referred to by u. The >>>> imports closure of a collection of RDF graphs is the smallest imports >>>> closed collection of RDF graphs containing the graphs." >>>> >>>> Neither of these specs require the URI/IRI of an ontology (or for a >>>> named graph in the case of SPARQL) to be dereferenceable on the Web, >>>> but >>>> this is - IMO intentionally - left open in the specs, just mentioning >>>> that the URI/IRI at identifies a graph/ontology. How this >>>> identification >>>> is specified is not part of the specs. While accessing the URI as a URL >>>> from the Web might be the default behavior, there are use cases where >>>> this may not be desirable (e.g. in a Triple store which has several >>>> named graphs stored, these graphs may not be (web) accessible, but only >>>> be called by these "names" within the triple store.) >>>> >>>> Likewise, I would be reluctant if we made any stronger assumptions >>>> here, >>>> which might be restrictive. I rather suggest to adopt something similar >>>> to the formulation in OWL above. >>>> >>>> Long written, briefly summarized: >>>> I suggest to replace >>>> "accessible from the locations u1,...,un" >>>> by >>>> "referred to by u1,...,un" >>>> >>>> >>>> This is though not directly related to your question, I see. But we >>>> could state e.g. something like "If there is no RDF graph (or, resp. >>>> ontology) referred to by uri u_i in an imports statement, the >>>> respective >>>> graph SHOULD be treated as empty." (in case this is the behavior we >>>> want to advocate) >>>> >>>> Axel >>>> >>>> 2. http://www.w3.org/TR/owl-semantics/direct.html >>>> 3. http://www.w3.org/TR/rdf-sparql-query/ >>>> 4. http://www.w3.org/TR/2008/WD-owl2-rdf-based-semantics-20081202/ >>>> Jos de Bruijn wrote: >>>>> In section 5.2 of the RDF-OWL document [1] we specify how RIF >>>>> documents >>>>> with two-ary import statements must be interpreted. however, we do not >>>>> say anything about the case that an import statement refers to a >>>>> location does not have an RDF graph. >>>>> >>>>> So, if >>>>> >>>>> Import(<u1> <p1>) >>>>> ... >>>>> Import(<un> <pn>) >>>>> >>>>> are the 2-ary import statements and one of u1,...,un does not point to >>>>> an RDF graph, what should happen? Do we say that the document >>>>> could be >>>>> rejected, or do we leave this unspecified? >>>>> >>>>> related: what if pi denotes the OWL DL profile, but ui does not >>>>> point to >>>>> an OWL DL ontology? Should the document be rejected? I think so. >>>>> >>>>> Best, Jos >>>>> >>>>> >>>>> [1] http://www.w3.org/2005/rules/wiki/SWC#Interpretation_of_Profiles >>>> >>> >> >> > > -- Jos de Bruijn debruijn@inf.unibz.it +390471016224 http://www.debruijn.net/ ---------------------------------------------- No one who cannot rejoice in the discovery of his own mistakes deserves to be called a scholar. - Donald Foster
Received on Tuesday, 17 February 2009 11:21:30 UTC