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Re: CURIEs: A proposal

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 28 Jun 2006 14:30:37 -0500
Message-Id: <p06230901c0c87ecf3eef@[10.100.0.28]>
To: "Paul Prescod" <paul@prescod.net>
Cc: "Harry Halpin" <hhalpin@ibiblio.org>, www-tag@w3.org

>Wouldn't you say that if "you" (in the human or 
>machine sense) create a URI to name somethign 
>then you must know SOMETHING about what you were 
>trying to name.

Sure, it sounds reasonable.

>If the thing you are naming is "HTML" then you 
>know that "HTML" stands for "Hypertext Markup 
>Language". If the thing you are naming is a 
>product, then perhaps you know the MSRP.

Sure, but I don't want to admit that there is 
likely to usually or often be a nice tidy 
universal code for things being named. Most of 
the time there won't be.

>On 6/27/06, Pat Hayes <<mailto:phayes@ihmc.us>phayes@ihmc.us> wrote:
>
>
>What they mean is determined by the totality of assertions that are
>made using them, and there is no way to access all of that by any
>kind of dereferencing. The idea that a single URI can locate an
>'authoritative' or 'defining' piece of (say) OWL or RDF which is the
>single best source for what the URI means, is unsupported by any of
>the SW specs, false in many widely deployed cases (FOAF, Dublin
>Core), at odds with the open nature of the Web, and IMO harmful.
>
>
>The referent need not be authoritative or 
>defining (though it often might be). It is 
>enough that it be informative.

Er.. I was using 'referent' to mean the thing 
referred to, rather than a description. But if 
you mean what I think you mean here, I agree.

>Im sure it can often help, but a problem arises when someone insists
>that there *must* be something there, because there are going to be
>many cases where it is hard to impossible to provide anything useful,
>so what will be provided will in fact not be useful, but providing it
>will nevertheless absorb a lot of effort, the cost of which is a
>brake on development and deployment.
>
>
>This is the heart of the argument. What examples do you have?

Take almost any URI reference in any OWL ontology, for example

http://www.w3.org/TR/2003/PR-owl-guide-20031209/wine#madeFromGrape

Now, what that *means* is a binary relation 
between wines and grape types. There is no way to 
put that meaning at the other end of a 
dereferencing process. One could of course - and 
this is what is currently usually done - put the 
OWL/XML ontology itself at the other end of the 
base URI in cases like this, but that isn't 
actually necessary to the way that the ontologies 
function; it is just a kind of obvious convenient 
default thing to do when there is nothing better 
to do. But that doesnt handle the #madeFromGrape 
properly, and as the TAG ruling on http-14 has 
shown, this idea can itself cause a lot of 
trouble and strife. And the main point is that 
there is no actual *need* to put anything there 
in cases like this. The SWeb software which is 
designed to use URIs like this will never try to 
dereference them. That isn't what they are for.

>I could understand the argument that it is 
>sometimes hard to provide anything at all 
>(because providing anything at all requires a 
>web server). But why would it be hard to provide 
>something meanginful? Why did you create a name 
>for something about which you know NOTHING?

No, that is not the point. I know a lot about it 
(let us suppose) which is why Im writing an 
ontology. But the connection between this name 
and its ontology is not that the latter is at the 
other end of an HTTP GET starting with the 
former, it is that the ontology *contains* the 
name itself. It is the surrounding text which 
embodies the meaning, not something at the other 
end of a Web dereferencing process. The name, in 
cases like this, gets it meaning from the way it 
is used inside what amounts to a large data 
structure, which is the RDF graph of which the 
OWL/XML text document is a handy rendering 
(representation, in the REST sense?). The Web is 
relevant to this only insofar as it allows these 
graphs/texts to be transmitted, combined and 
used, but it adds nothing to the way that the 
graphs/texts determine the *meaning* of the names 
which occur in them.
To make the point more forcefully: Imagine an OWL 
ontology located at http://ex.place/foo.html 
which when you look at it you discover that all 
the names in it have the base URI 
http://ex:otherplace/baz. This might be slightly 
discourteous, but it is perfectly legal and would 
not cause any SWeb engines to miss a beat. In 
fact, most of them wouldn't even be aware of it. 
And as for human readers, if they are looking at 
the name, then they are already looking at the 
text which tells them as well as anything can 
tell them what the name means, viz. the text of 
the ontology itself.
>  >It helps  to make the Web be "self-describing", although the notion of
>>"self-describing" is something I think is another notion that could
>>really use some inspection.
>
>I'd sure like know what it means, myself :-)  Can you elaborate?
>
>
>Self describing means that a reader can start by 
>looking at some data and follow links backwards 
>to the specifications that define the intended 
>meaning of the data.

Yes, I thought that was perhaps what it was 
supposed to mean. Tim BL explained this idea to 
me a few years ago. I don't buy it. First, its 
just not true, and the Web seems to work just 
fine whether its true or not, which suggests it 
is more dogma than theory. Second, are we talking 
here about human readers or software? The SWeb is 
supposed to be usable by software agents which 
are not usually capable of reading a W3C spec 
document and wouldn't be able to do anything with 
it even if they could. In fact, most human 
readers are in the same position most of the time.

>With raw XML, the tags are "links" to English word meanings

XML tags are linked to English word meanings??? 
Where are these word meanings, and how does one 
link to them? Do they have URIs?

>which are much more helpful than bit patterns. 
>With (for example) HTTP-identified namespaces 
>you have actual links to resources that might 
>describe the meanings of the words in a human or 
>machine-processable language.

Might, yes. In fact do, only rarely. And as I 
say, it doesn't seem to matter a tinkers toss 
whether they do or not.

>In short, a self-describing message or document 
>points from the message towards the spec whereas 
>most messages or documents require you to find 
>the message or document using some out-of-band 
>mechanism. "This file starts with the characters 
>MZ. I wonder what file type this is?"

I find the best way to find out is usually to try 
Google. So, is this a Web architectural principle 
at work? Is Googling a kind of link following?

Pat

>
>  Paul Prescod


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Received on Wednesday, 28 June 2006 21:10:13 GMT

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