- From: Libby Miller <Libby.Miller@bristol.ac.uk>
- Date: Tue, 29 Jan 2002 19:45:27 +0000 (GMT)
- To: www-rdf-comments@w3.org
hi, Someone pointed out Dan Connolly's post about querying and datatypes to me [1]. I think the case he's refering to is where there is no intervening node representing the value of the datatype, but literals can have datatypes imposed by range contraints, i.e. TDL 'global idiom'. SquishQL in Inkling uses (1) the triplesmatching-type api call (2) the triples generated from a parser to make its queries. It is built on top of the triples-matching style API and will probably do whatever that does, or fit rounds it...however: In general, I'd do a query over typed nodes like this select ?x ?y ?z where (?x <dc:Title> ?y) (?z <age> ?y) (?z <rdf:type> <foaf:Person>) (say) although usually this will be enough: select ?x ?y ?z where (?x <dc:Title> ?y) (?z <age> ?y) In my experience, usually you don't care what the type of a node is; sometimes you do, and then you can add the extra constraint. This doesn't work in TDL 'global idiom' when the datatyping is only mentioned in rdfs:range. If it was in the database somewhere you could have select ?x ?y ?z where (?x <dc:Title> ?y) (?z <age> ?y) and the constraint on ?y from the range would be implicit and would happen somewhere in the application code. In that case I'd be against this idom, because normally I don't rely on having the schema (or schema-like constraints) available when you make a query, and because I prefer to make explicit queries. Also I think that I would probably put the emphasis the opposite way to the way Dan C suggests in the 'duh' argument - that is, in the absence of typing info I'd make a match. Maybe that would be wrong. The TDL 'local idiom' looks alright to me. I guess if there are many possible lexical representations of a given literal, then that might make querying more fiddly. At the moment tests like ?x > 5 are done by casting to Java datatypes, as Andy does with RDQL as well, so matching different lexical representations is avoided. I hope this makes sense: the more I read the datatypes info from rdf-core, the more confusing I find it, though Brian's summary was helpful [2]. The names of the different proposals seemed inconsistent and confusing to me coming to the discussion rather late. Libby [1] http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Jan/0358.html [2] http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Jan/0357.html
Received on Tuesday, 29 January 2002 14:46:45 UTC