- From: Richard Cyganiak <richard.cyganiak@deri.org>
- Date: Fri, 13 Aug 2010 12:08:43 +0100
- To: Ivan Herman <ivan@w3.org>
- Cc: "Toby Inkster" <tai@g5n.co.uk>, public-rdfa-wg@w3.org
On 13 Aug 2010, at 09:33, Ivan Herman wrote: > You say Toby's examples below are compelling, and he definitely > argues for keeping the current structure for prefixes. Do you > propose to have a different approach for terms than for prefixes? I would be ok with having different approaches for establishing term mappings and prefix mappings. They do different things, after all. > You also said (in your other mail) that you do not feel Toby's > arguments are valid for terms, only for prefixes. To change his > examples a bit: if I have a term definition > > <http://www.ex.org/vocab/1.0/MyTerm> rdfa:term "exampleTerm" . > > and, through some evolution of the vocabulary we have a 2.0 version, > but this has a bridge of the form > > <http://www.ex.org/vocab/1.0/MyTerm> owl:sameAs <http://www.ex.org/vocab/2.0/MyTerm > > . Term mappings are used with classes and properties (and datatypes). For classes and properties, OWL has specific mechanisms -- owl:equivalentClass and owl:equivalentProperty -- which do not have the effect of “copying” statements like rdfa:term over from one entity to the other. For datatypes, using owl:sameAs is just asking for trouble. So the use of owl:sameAs on the URIs involved in a term mapping is likely an authoring mistake, and certainly bad practice. That being said, I still don't see any major problems arising from it for RDFa, see below. > That, actually, means that I can also deduce a triple of the form > > <http://www.ex.org/vocab/2.0/MyTerm> rdfa:term "exampleTerm" . > > So how do we handle that? So if you apply OWL reasoning to the profile document, you get: <http://www.ex.org/vocab/1.0/MyTerm> rdfa:term "exampleTerm" . <http://www.ex.org/vocab/2.0/MyTerm> rdfa:term "exampleTerm" . This just means the profile author has established a mapping of the same term to two different URIs. I suppose the RDFa draft already specifies how to handle profiles like that? I read the document but couldn't tell -- this needs to be tightened up in the document IMO, and that should then take care of the owl:sameAs issue. > Unless we can, somehow, formally _restrict_ the effect of an > rdfa:term predicate on a specific graph somehow (that may be a > possibility but I am not 100% sure how to do that, but maybe we > can), this may create the same type of issues as the ones Toby is > referring to. You say it “may create the same type of isses”. Well, does it or does it not? If it does, example please. If not, let's move on. > So. Trying to move forward... The RDFa Core document is already > juggling with the term "graph". It talks about default graph, the > processor graph, etc. Ie, we can very well refer to the profile > graph for a specific document. We could then make it very explicit > in the RDFa Core spec that only those triples are considered that > are part of that graph; this would take away this problem (as well > as Toby's problem). Yes, we are bringing a closed world in through > the back door:-) This is in effect *already done* in the current draft, although without using the word “graph”: “Attempt to retrieve the content of the URI … parse the retrieved content as an RDFa document … extract the triples into a collection associated with that URI. Note: These triples must not be co-mingled with the triples being extracted from any other URI.” “It is possible that a referenced RDFa [profile] document will in turn reference other documents via @profile. Regardless of the depth to which such references might go, only the triples in the top level document effect current processing.” http://www.w3.org/TR/2010/WD-rdfa-core-20100803/#s_profiles I agree that the RDFa Profiles section could be improved by consistently using a term like “profile graph”, replacing phrases such as “extract the triples into a collection” or “for every extracted triple”, regardless of the URI/literal issue discussed above. Best, Richard > I must honestly admit that I still feel uneasy about the change, > though. But trying to find a way forward... > > Ivan > > >> >> Best, >> Richard >> >> >>> >>> Ivan >>> >>>> Best, >>>> Richard >>>> >>>> >>>> On 12 Aug 2010, at 10:24, Toby Inkster wrote: >>>> >>>>> On Fri, 6 Aug 2010 07:40:04 +0200 >>>>> Ivan Herman <ivan@w3.org> wrote: >>>>> >>>>>> This was discussed several times on the mailing list and I fully >>>>>> understand your issues. Here is the reason I was in favour of the >>>>>> current setup, but I am absolutely open to discussion because, >>>>>> well, >>>>>> it does complicate processing (speaking as an implementer). >>>>> >>>>> FWIW, I agree with your reasoning for the current vocab. Prefix >>>>> and term >>>>> mappings are semantically a relationship between two strings. >>>>> >>>>> Imagine this: >>>>> >>>>> <http://xmlns.com/foaf/0.1/> rdfa:prefix "foaf" . >>>>> >>>>> Now, the following is also true (probably): >>>>> >>>>> <http://xmlns.com/foaf/0.1/> >>>>> a owl:Ontology ; >>>>> owl:sameAs <http://dbpedia.org/resource/FOAF_(software)> . >>>>> >>>>> Thus it follows that: >>>>> >>>>> <http://dbpedia.org/resource/FOAF_(software)> >>>>> rdfa:prefix "foaf" . >>>>> >>>>> Thus an RDFa processor could expand 'foaf:name' to: >>>>> >>>>> <http://dbpedia.org/resource/FOAF_(software)name> >>>>> >>>>> Which we wouldn't want to happen. >>>>> >>>>> In RDF terms, when we're defining prefixes and terms we're not >>>>> describing the underlying resources - we're just talking about >>>>> the xsd:strings. We're not even talking about xsd:anyURIs, because >>>>> say, "htt" is a valid expansion for a prefix, which might be used >>>>> as follows: >>>>> >>>>> prefix="h: htt" >>>>> property="h:p://xmlns.com/foaf/0.1/" >>>>> >>>>> So I'd recommend keeping the current pattern, though I think the >>>>> range of rdfa:uri should be changed to xsd:string for the above >>>>> reason. >>>>> >>>>> Another argument against switching to >>>>> >>>>> <http://xmlns.com/foaf/0.1/> rdfa:prefix "foaf" . >>>>> >>>>> would be the fact that you'd lose the owl:FunctionalProperty- >>>>> ness of >>>>> rdfa:prefix and rdfa:term. >>>>> >>>>> -- >>>>> Toby A Inkster >>>>> <mailto:mail@tobyinkster.co.uk> >>>>> <http://tobyinkster.co.uk> >>>>> >>>>> >>>> >>> >>> >>> ---- >>> Ivan Herman, W3C Semantic Web Activity Lead >>> Home: http://www.w3.org/People/Ivan/ >>> mobile: +31-641044153 >>> PGP Key: http://www.ivan-herman.net/pgpkey.html >>> FOAF: http://www.ivan-herman.net/foaf.rdf >>> >>> >>> >>> >>> >> >> -- >> Linked Data Technologist • Linked Data Research Centre >> Digital Enterprise Research Institute (DERI), NUI Galway, Ireland >> http://linkeddata.deri.ie/ >> skype:richard.cyganiak >> tel:+353-91-49-5711 >> >> > > > ---- > Ivan Herman, W3C Semantic Web Activity Lead > Home: http://www.w3.org/People/Ivan/ > mobile: +31-641044153 > PGP Key: http://www.ivan-herman.net/pgpkey.html > FOAF: http://www.ivan-herman.net/foaf.rdf > > > > > -- Linked Data Technologist • Linked Data Research Centre Digital Enterprise Research Institute (DERI), NUI Galway, Ireland http://linkeddata.deri.ie/ skype:richard.cyganiak tel:+353-91-49-5711
Received on Friday, 13 August 2010 11:09:21 UTC