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Re: [ontolog-forum] OWL and lack of identifiers

To: "[ontolog-forum] " <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Bill Andersen <andersen@xxxxxxxxxxxxxxxxx>
Date: Mon, 16 Apr 2007 22:11:39 -0400
Message-id: <F018FE6E-40CA-4745-97FF-0ED18156B637@xxxxxxxxxxxxxxxxx>

On Apr 16, 2007, at 22:04 , Waclaw Kusnierczyk wrote:

The problem is whether 'www.nonsense.no' is a valid instance of 'host', 
which depends on whether 'nonsense.no' is registered with IANA to 
correspond to an allocated IP address.  If it is registered, then I can 
agree that this is syntactically valid.  If is not registered, one can 
argue that it is not even "syntactically valid", because valid domain 
names are determined by IANA registry, not by a production rule.  That 
is, the requirement is not just that it is well-formed, but rather that 
it is in a particular list of valid strings.  By way of analogy, 
consider a language in which symbols must be declared before they are 
used. If the parser encounters a well-formed lexical object that should 
be a declared symbol but the "symbol table lookup" fails (the symbol was 
never declared), is that a "syntax error"?  Is that text "syntactically 
valid"?  (I don't know that the formal languages community has 
consistent terminology in this area, but I haven't written a compiler in 
over 20 years.  Maybe they do now.)

We may be splitting hairs here.

A formal language is a set of strings over an alphabet -- a set of 
symbols.  You may define the language ostensibly, by listing all the 
strings, which would imply which symbols are in the alphabet.  You may 
define the language by means of a grammar, that is, specify the alphabet 
and rules for forming strings in the language.  You may do both, but the 
definitions must agree.

I agree with Wacek on this.  What's being suppressed in Ed's discussion is precisely a difference between syntax and semantics.  That 'www.nonsense.no' is syntactically valid is not in question - that such a string is a "registered" name is a semantic (and relational) property ... of names.

Bill Andersen (andersen@xxxxxxxxxxxxxxxxx)

Chief Scientist

Ontology Works, Inc. (www.ontologyworks.com)

3600 O'Donnell Street, Suite 600

Baltimore, MD 21224

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