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Re: Comments on ioctl (was: Re: big issue (2001-09-28#13))

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Mon, 8 Oct 2001 19:45:09 -0500
Message-Id: <p05101019b7e7f156af2e@[205.160.76.193]>
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
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Received on Monday, 8 October 2001 20:45:20 EDT

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