- From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
- Date: Fri, 15 Feb 2002 14:54:17 -0500
- To: phayes@ai.uwf.edu
- Cc: www-webont-wg@w3.org
From: Pat Hayes <phayes@ai.uwf.edu> Subject: Re: REQDOC: reification Date: Fri, 15 Feb 2002 01:11:08 -0500 > >One of the requirements in the requirements document is the ability to > >associate properties with statements. This would require, at least, > >some version of reification of statements, and to work right would require > >a way of referring to statings. > > > >RDF has made a total hash of reification. > > I don't agree. RDF certainly screwed up in some ways. It is > incomplete, and the M&S is confused and ambivalent between divergent > readings, but the general idea is sound, if rather simple, and the > use cases that we have been able to discover all pretty much converge > on one of the two plausible readings of the M&S wording, so the WG > will probably give a reasonably clear ruling on this soon. So its not > a total hash. It is pretty useless, in my view, but some people can > use it coherently and seem happy with it. Well, there is a document (RDF M&S) that says one thing (every statement has exactly one reification), is often read as another (there can be any number of reifications for a statement), and is used in a third way (a reified statement corresponds to a stating). What else can this be but a hash? > >The RDF Core WG is trying to fix > >this a bit, but it is probably out of their scope to make any significant > >improvment (as opposed to significant fix). > > > >I think that adding reification to OWL would be, at best, a significant > >research project and, at worst, a black hole. > > I think that what might be called simple object reification - the > ability to describe syntactic object tokens, including those of the > language itself, and some kind of external referential linking > mechanism analogous to ostensive pointing to an expression token - is > quite do-able, raises no deep black-hole issues (notice I carefully > did not say 'tr*th pre*d*c*te' ) and provides about 90% of the > practical functionality needed by enthusiasts of reification. So I > think that something useful can be done pretty easily. It will be > moderately trivial from a FOM perspective, for which we should all > breath sighs of relief. Well, yes, if all you want is some syntax (rdf:Statement, rdf:subject, rdf:predicate, rdf:object) that has no other meaning, then go ahead. I would say this gets about 0% of the practical functionality of reification with about 0% of the effort. If users of RDF want to use the non-existent functionality of this syntax to hang any outside-of-RDF reification onto then they can. But why then make all this part of RDF? You aren't getting anything for it from RDF (except, maybe, a gentleman's agreement to use the same URIs). > >In any case, I don't see the motivation for the ability to associate > >properties with statements (in the OWL logic, at least) from the shared > >ontologies goal. Surely it is possible to share ontologies without > >associating properties with statements. > > The real use case is associating them with statings, ie *tokens* of > expressions in ontology documents. And that is needed in for example > date-stamping, tracking provenances, that kind of thing. Yes, sure, but how does RDF reification help in this? Futher, this is not a ``sharing ontologies'' motivation any longer. > Pat Hayes [...] Peter F. Patel-Schneider Bell Labs Research
Received on Friday, 15 February 2002 14:55:47 UTC