- From: Pat Hayes <phayes@ai.uwf.edu>
- Date: Mon, 4 Feb 2002 17:32:28 -0600
- To: w3c-rdfcore-wg@w3.org
Guys, Ive been trying to write a followup to the 'bermuda triangle' message, and its still in an incomplete state, but I thought it might be worth giving y'all the URI in any case as time is so short: http://www.coginst.uwf.edu/users/phayes/DatatypesUnifiedMT-draft1.html I will be updating this when I get a chance, maybe tonite. (Maybe. The html is a crock, so ignore the colors, font sizes etc.; and its a bit repetitive because I was writing it in streaming mode. ) In sum: one can have the TDL syntactic idioms without having pairs in the MT, and the local and 'range' typing all work together smoothly and many of the proposed alternative idioms all work together and in fact are semantically equivalent, and literal nodes are tidy, and literals denote strings. That's the simple version. What this does not handle, however, is the case where a literal is used in-line (no bnode) to refer to a value; in this simple mode, <mary> <age> "10" . says that Mary's age is a character string, and there's no arguing about it; if you assert some range info on <age> that disagrees with that, then you are just plain wrong. Or, there is another option, which handles all the other idioms in just the same way and gives them the same meaning, but where a bare in-line literal with no typing information is under-determined; it means pretty much the same as a bnode, by itself. This 'subtle' option handles all the datatyping idioms that have been proposed so far (I think), but it requires some complications. First, we have to allow graphs to be untidy on literal nodes (cost: need to extend N-triples notation in some way to indicate whether or not two occurrences of a literal are on the same node.). Second, it is almost impossible to make range-typing work on arbitrary datatypes unless we allow literals to be subjects. (Cost: literals as subjects, which some users will not like, eg might break DAML compatibility.) Third, some queries and rules might turn out to have a stronger meaning than people currently expect, and so have some unexpected conclusions , cf discussion near end of document. (Cost: I don't think this last is a fatal problem, in fact, but it might ruffle some feathers.) Finally, this proposal has some overall costs. It uses a new namespace http://www.coginst.uwf.edu/users/phayes/rdf-datatype-schema.html and requires that it be used intelligently. (You really only need the datatype and type, the rest are for being fancy-schmansy.) And it requires imposing some semantic conditions that go beyond what can be stated using closure rules; which is another way of saying that this is a genuine semantic extension to RDF; it can't be thought of as just an abbreviated form of a whole lot of RDF triples (as RDFS can, for example.) Datatyping this sensitive really does go slightly beyond what can be said *in* RDF, in a sense. I would argue that this is inevitable if we are going to deal properly with XML datatypes, but I can see that some folk will be worried by it. Anyway, I offer it for consideration/comment/trashing/whatever. I'll try to summarize what it does for all the 'issues' soon. However, a quick comment about issue B4 in V4. When writing things like _:f <rdf:title> <film> . _:f <dc:title> "10" . <mary> <age> "10" . you have to say whether those are the same literal NODE or not. Graphs can be untidy on literal nodes, so this is ambiguous (4 nodes or 5 in the graph?). And it matters, because one gets different entailments in the two cases. If those "10"s are the same literal node than this entails _:x <cd:Title> _:y . _:z <age> _:y . but if they are not the same node, and if nodes can be typed separately, then it doesn't, in general. Either way the inference is quite clear, but the discussion is confused because the Ntriples *syntax* is ambiguous when literal nodes are not tidy. Pat -- --------------------------------------------------------------------- IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola, FL 32501 (850)202 4440 fax phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes
Received on Monday, 4 February 2002 18:31:55 UTC