- From: Pat Hayes <phayes@ai.uwf.edu>
- Date: Mon, 8 Oct 2001 19:45:09 -0500
- To: Martyn Horner <martyn.horner@profium.com>
- Cc: w3c-rdfcore-wg@w3.org
>Pat Hayes wrote: > >>a literal is a name whose denotation can be computed from the name alone > > >Maybe I missed something in the argument but does `denotation' >distinguish between numerals (literals) denoting numbers and >numerals (literals) denoting, say, dates. So the literal "20001225" >has, at least, two denotations? Does this invalidate this >definition? Do you mean `unique denotation'? If you don't, how does >this definition stay valid? Ye, I do mean unique. See below for the consequences. > >As I suggest, I think I may be completely off-track in asking this. No, dead on track, I think. My answer would be (I'm coming to realize how much of a minority view this is, though) that the whole notion of being a literal (in fact, of being a denoting name of any kind) is that there is enough structure in the 'logical syntax' - the syntax that the model theory is attached to - to determine a unique referent in any interpretation. Without that assumption, semantics just doesn't work: there is no way to know that the same token used twice has the same meaning. (Exceptions to this are much discussed in 'real' linguistics, like indexicals ('here', 'now') and demonstratives ('that', said while pointing at something), but in order to give a coherent semantics to things like these one has to restore uniqueness of reference by introducing things like explicit contexts, communication situations, possible worlds and other exotic paraphinalia.) Now, taking the above idea of a literal seriously, this in turn would require that the 'logical syntax' has to provide enough information to distinguish literal numerals from literal dates from literal house-numbers, etc. , if you want these all to be literals, anyway; that is, if there are two senses of "20001225" under which it has different literal values, then that quoted thing isn't a literal: it's only part of a literal. The complete literal is that string together with *something* that tells us which sense of it is intended (as an integer, as a street number, as a date, whatever). Exactly what the 'something' is, I would claim total agnosticism about, only that it is somehow syntactically specified: it has to be something that could be determined by a parser; ideally, by a lexicalizer. Hypertext provides a brave new world of ways of specifying such things; maybe it is hidden in some piece of metadata markup, or a DTD someplace; or maybe it is written right there next to the string of characters. Whatever; that's to do with the concrete syntax in some lexicalization. In the graph syntax, I would suggest, we treat it more abstractly, and just say that the literal label in the graph is *something* that has the can-compute-unique-referent-from-label property. Which is what I tried to do (without getting into the issue of it being computable, which seemed too controversial for the MT document) by having LV be a *globally* fixed mapping, ie one that is not dependent on the particular interpretation. Which, by the way, is exactly what Peter Patel-Schneider is currently roasting my feet over the fire about, for exactly the reason you raise: he doesn't want literals to be forced to have a single global meaning in DAML. If I thought that 'literal' meant simply 'character string'. I would agree with him (and I suspect, you), but I have never thought that it did mean that. Maybe I was wrong, though, in this community; and if so, then I should probably change the model theory, or at least the way it is worded. However, if literals really are just character strings, then I don't really see any coherent way of allowing a single bare character string to have a number of different literal values. If "20001225" really could mean either a bit more than 20 million or Xmas day, surely *something* has to be able to decide which one is meant, when one comes across that string in a graph somewhere? 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, 8 October 2001 20:45:20 UTC