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Re: What do the ontologists want

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 15 May 2001 10:44:11 -0500
Message-Id: <v04210102b726f5783696@[]>
To: "Jonathan Borden" <jborden@mediaone.net>
Cc: www-rdf-logic@w3.org
>pat hayes wrote:
> > Can you (or anyone) say why the ability to quote is considered a
> > practical necessity? From where I am standing it seems an arcane and
> > exotic ability, not one that is of central practical importance. What
> > is the practical utility of being able to refer to a predicate,
> > rather than use it?
>What is arcane or exotic about the ability to say:
>'Jon says "The sky is blue."' ?

It is logically exotic, if I may be forgiven the terminology, since 
it refers to a sentence by ostention, rather than by denotation. 
Actually, even this is relatively harmless, as long as you simply 
quote. However, in order to be useful, one usually has to be able to 
move between a quoted sentence or expression and the use of that 
sentence or expression as part of the language itself, and this 
'reflexion' is what is really arcane and tricky. Simple quotation is 
relatively harmless, I concede, but largely useless: it is simply a 
way of referring to character strings.
For example, would you want to be able to infer, from your example, 
that Jon said that the sky is blue? It doesnt follow from it, 
however, unless you provide some machinery to de-quote a quoted 
string. Seems to me that the latter is much more useful than the 
former: the relationship between an agent and the *content* of what 
they say is more interesting, usually, than the relationship between 
the agent and the *form of character strings* that they use (except 
of course when the mapping between form and meaning is central to the 
discussion, as it is in some legal settings; but again, this seems 
exotic for our purposes.) To refer to the content of an expression, 
however, one does not quote it: one simply uses it.

>It is the most complex type of statement my 18 month old daughter is able to
>make. Literally she recently said: "Grandma say 'Sarah did dat!'" which was
>true, or so I say :-)

Well, first, even 18 month old humans are a damn sight smarter than 
any machines we know how to build, particularly when it comes to 
language. But second, I would guess that what she actually meant was 
that Grandma uttered a certain sequence of phonemes. She wasnt really 
quoting in the sense that is indicated by those symbols " " on the 

>In any case, the ability to create a reference to something has proven
>itself useful in my practical experience.

Sure, but be careful what you mean by 'reference'. A pointer to a 
position in a data structure is one kind of reference; a name 
denoting an entity is a different notion of reference. Both are 
useful, but trouble ensues if you use one for the other carelessly. 
Quotation creates a name (of a character string), not a pointer.

>The reason I have suggested that quotation be implemented in a fragment
>identifier syntax is that URI references are how we refer to things on the
>web, and a statement is one of the things we might want to refer to.

I confess to still not knowing what a URI is supposed to be beyond a 
URL, and not believing what I have read about them. URLs are file 
addresses, a species of pointer, and those I do understand. URLs do 
not denote what they point to. The relationship between a URL and the 
file it locates is not the same as that between a logical name and 
what it denotes (for example, the locatee is not determined relative 
to an interpretation, but is fixed by the operational circumstances.)

>Quotation is related to query and in the same way as XPath serves as a
>simple query language for XML,

I beg to differ. XPath provides a way to refer to a position within 
an expression, which is exactly what quotation does not provide. 
Quotation simply refers to the quoted expression as an atomic whole, 
and provides no way to access its structure, syntax, parts or 
anything else. If you want to do that, you need something like 
quasi-quotation (an extended form of quotation invented by WVO Quine 
which allows quantification over substrings inside quoted 
expressions), and if you want to be able to refer to the *content* of 
quoted expresions, then you also need something that maps between 
descriptions of expressions (such as quoted strings) and the actual 
expressions that those descriptions describe; what is usually called 
a truth-predicate. Bottom line: in order to be useful, quotation 
needs to be supercharged and be supplemented with truth-predicates 
(or principles of reflexion, or various other exotic pieces of 
linguistic machinery).

>an RDF path language might serve as a simple
>query language for RDF. For example:
>?x says "The sky is blue"

OK, if you bear in mind that this really does mean only that ?x says 
a certain string of characters. It (quite literally) says absolutely 
nothing about skies being blue, not even that ?x said that. If you 
want to say that ?x asserts that the sky is blue, you need something 
which can map back from the quoted string "The sky is blue" to 
whatever proposition that quoted string is asserting in whatever 
language ?x is talking in.

I'm not saying that this can't all be done. I am saying that it is 
exotic, not simple, and requires elaborate syntactic and semantic 
machinery to be done without producing paradoxical results.

Pat Hayes

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Received on Tuesday, 15 May 2001 11:44:16 UTC

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