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

To: edbark@xxxxxxxx
Cc: Ontolog Forum <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Waclaw Kusnierczyk <Waclaw.Marcin.Kusnierczyk@xxxxxxxxxxx>
Date: Wed, 18 Apr 2007 09:50:41 +0200
Message-id: <4625CDD1.80801@xxxxxxxxxxx>
One more terminological note:    (01)

It is confusing to say that an XML document is well-formed in the sense 
of its conformance to the XML syntax, since:    (02)

- this way of speaking is suggestive of that there can be a 
non-well-formed XML document (where 'well-formed' still refers to the 
XML syntax), while
- a document that does not conform to the XML syntax simply is not an 
XML document.    (03)

It makes sense to speak of a valid or invalid XML document, though, with 
'valid' referring to another syntax definition (xslt schema/dtd, say). 
But, again, to say that an xslt document is valid, with 'valid' 
referring to xslt syntax, is equally redundant.    (04)

vQ    (05)

Ed Barkmeyer wrote:
> Wacek,
> you wrote:
>> I was actually curious whether you will refer to the XML example.
>> The use of 'well-formed' and 'valid' here are synonymous in that both 
>> are used to speak of a document's conformance with a grammar;  
> With that definition, the terms are equivalent, yes.  One can distinguish:
>   well-formed/valid with respect the XML grammar
> from
>   well-formed/valid with respect to the DTD/schema
> But XML chooses to use 'well-formed' for the first, and 'valid' for the 
> second.
>> equally well it might be said that a document is valid as a XML 
>> document and well-formed as an RDF document.  This is just a 
>> terminological convention.
> Exactly.
>> The issue with IANA is a bit different, in that a domain name may be 
>> registered and unregistered, i.e., its status as valid or not may 
>> change, though the rules of the language do not change, in general.  
> An interesting point.  This is a big difference between a registry of 
> values and an enumerated list.  The validity of a symbol is 
> time-dependent, and related to events out of the context of the usage.  
> So my earlier analogy with local symbol definitions, which are solely 
> dependent on other elements of the context of use, is inappropriate.
>> On the other hand, a document that is XML-well-formed and XXX-valid 
>> remains well-formed and valid, unless the grammars are redefined.  
>> (You might say that a change in IANA registry is, analogously, a 
>> change in the languages rules, if you insist.)
> I agree that is stretching the point.  The time-dependency is, to me, a 
> good reason for discarding the idea that "hostname validity", in the 
> sense of being registered, is "syntactic".
>> The issue is that in the case of XML the use of 'well-formed' for the 
>> one and 'valid' for the other is well-defined and documented.  In the 
>> case of URLs, I am not sure whether there is an officially established 
>> convention of calling a URL 'well-formed' if it conforms to the RFC 
>> and calling it 'valid' if it is registered;  maybe there is, but maybe 
>> this is only wishful thinking.
> Upon examination, RFC 1123 refers to "syntactically valid" hostnames as 
> those conforming to the production rules.  Beyond that, the rest of the 
> terminology is all wrapped up with the DNS protocols and failure modes.  
> There really isn't a concept of "valid hostname"; the concept is "DNS 
> lookup succeeds". This is further complicated by the fact that the DNS 
> folk believe their mechanism can work for anything that supports URI 
> syntax (as long as the names are short enough), and therefore DNS is not 
> limited to hostname lookups.
> So I have to admit that there is nothing "syntactic" about the validity 
> of a hostname beyond its lexical rules.  After that, there is a process 
> that succeeds or fails in one of several ways.  The function of the 
> hostname in a URL is to identify one or more Internet hosts that MAY be 
> able to provide the service that maps the URL to a resource.  And the 
> mapping of hostname to host is properly seen as just part of the complex 
> process of performing the URL-to-resource mapping.
> I also have to admit that until just now, I hadn't looked at RFC 1123 
> for years, and I clearly should have, before creating a concept not 
> actually supported by the standards.  My apologies to all.
> -Ed
> P.S. I realize that this is one of those areas in which the "grey hair" 
> is not useful.  A certain implementation, with which I used to be 
> intimately familiar (15 years ago), talks about "valid host names", but 
> the standards don't.  More importantly, that experience predates HTTP as 
> the dominant Internet protocol;  the concept URL was just coming into 
> existence.  And in that time, one's tool did the hostname lookup to find 
> the IP address, and then inaugurated the application-specific protocol.  
> So "hostname validity" was a concept in its own right.  But the URL/URI 
> has made the "hostname" issue just a technical element of the "valid 
> URL" concept.  And in this "identifier" context, separating out the 
> "hostname" is inappropriate -- it is now a "lower-level concern".  I 
> just didn't realize until now that I'm still carrying old baggage in 
> this area.
>     (06)

Wacek Kusnierczyk    (07)

Department of Information and Computer Science (IDI)
Norwegian University of Science and Technology (NTNU)
Sem Saelandsv. 7-9
7027 Trondheim
Norway    (08)

tel.   0047 73591875
fax    0047 73594466
------------------------------------------------------    (09)

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