- From: Pat Hayes <phayes@ihmc.us>
- Date: Mon, 15 Nov 2010 08:58:46 -0600
- To: Graham Klyne <GK-lists@ninebynine.org>
- Cc: nathan@webr3.org, Semantic Web <semantic-web@w3.org>
Unfortunately correct :-) It might be worth pointing out that even plain literals in RDF effectively have a type already: they are character strings. So being 'untyped' should not be read as 'not yet having a type assigned' but more like 'known to have the type of a simple character string'. It is just like being typed with xsd:string, in fact. Thus, the example given by Nathan is already a type clash, and could give rise to an error (inconsistency) message from a type-savvy reasoner, since "12.2" is definitely not an xsd:decimal. Pat On Nov 12, 2010, at 6:59 AM, Graham Klyne wrote: > Nathan wrote: >> Hi All, >> I'd suggest that a high percentage of the worlds RDF data is being published untyped, where plain literals are used as rather than typed literals "12.2" vs "12.2"^^xsd:decimal, and also (to a lesser extent) "strings as"^^xsd:string's. >> Until today, I had assumed that it was pretty "safe" to, upon parsing, turn xsd:strings in to plain literals / pull the datatype from the range of a property and turn the object in to the correct type. >> However, it's been suggested to me today that this probably isn't a good thing / "the right thing" to do. >> And thus, should I be avoiding implementing this feature, and additionally what are the reasons *not* to do this. >> An example: >> Ontology contains.. >> ex:prop rdfs:range xsd:decimal . >> "data" contains.. >> :foo ex:prop "12.2" . >> What reason would there be not to just infer/pull the type and convert to a typed literal? > > Logical monotonicity. That is, adding new facts to an RDFgraph should not invalidate inferences already made. > > Attractive as it is, the mechanism you propose for inferring datatypes from rdfs:range declarations falls foul of this, as inferences you might make in the absence of rdfs:range statements may become incorrect when they are added to the graph. > > I see this is part of the price we must pay for supporting an open-world, "missing-isn't-broken" [1] system for data on the web. > > #g > -- > > [1] this phrase due to Dan Brickley - http://rdfweb.org/mt/foaflog/archives/2003/07/24/12.22.48/ - unfortunately that URI has gone 404 (Dan: is this uncoolness permanent or transient?) > > > > ------------------------------------------------------------ IHMC (850)434 8903 or (650)494 3973 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 mobile phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
Received on Monday, 15 November 2010 14:59:29 UTC