W3C home > Mailing lists > Public > semantic-web@w3.org > June 2007

Re: What if an URI also is a URL

From: Tim Berners-Lee <timbl@w3.org>
Date: Wed, 13 Jun 2007 11:15:58 -0400
Message-Id: <CB50BDAE-809C-48E9-9093-80B34C484B92@w3.org>
Cc: "M.David Peterson" <m.david@xmlhacker.com>, "r.j.koppes" <rikkert@rikkertkoppes.com>, "Yuzhong Qu" <yzqu@seu.edu.cn>, "Sandro Hawke" <sandro@w3.org>, <semantic-web@w3.org>, <swick@w3.org>, "John Black" <JohnBlack@kashori.com>
To: Pat Hayes <phayes@ihmc.us>


On 2007-06 -11, at 17:09, Pat Hayes wrote:

> Tim, as this discussion gets to the heart of what Ive been trying  
> to argue for several years, please take the comments below as  
> intended in a spirit of analysis rather than just pins and angels.

Ok.  [takes a deep breath].  I'll go down this path with you.

>
>> On 2007-06 -11, at 13:53, John Black wrote:
>>
>>>
>>> Tim Berners-Lee wrote
>>>>
>>>>
>>>> On 2007-06 -09, at 21:22, M. David Peterson wrote:
>>>>
>>>>> On Sat, 09 Jun 2007 07:13:52 -0600, Tim Berners-Lee <timbl@w3.org>
>>>>> wrote:
>>>>>
>>>>>> No. It cannot identify both a document and a person.
>>>>>
>>>>> Tim: Will all due respect... WTF?
>>>>
>>>>
>>>> I am using the 'identify' in the strict sense of 'denote'.
>>>> The semantic web is like a logic language in which URIs are  
>>>> symbols.
>>>
>>> Do you believe that by claiming to use the strict, logical sense  
>>> of the word 'denote' you thereby cause or require such  
>>> denotations to be absolute and unambiguous? Where do think  
>>> denotations (or identifications) come from?
>>
>> The architecture is that each URI is owned.
>
> OK
>
>>  With HTTP URIs, this happens through the domain name system and  
>> often  delegation within a domain. Unlike a word, a URI has an  
>> owner.  The owner attempts to make enough information available  
>> that the URI can be used by others without ambiguity in practical  
>> situation.
>
> Well now, several points. First, do owners in fact do this? I havnt  
> seen a great deal of such information-providing going on, myself.  
> But OK, fair enough: perhaps you mean, they SHOULD make such  
> information available. But second, more seriously, HOW would they  
> do this? Take your example:
>
>> For example, W3C owns http://www.w3.org/People/Berners-Lee/card#i  
>> and has delegated to me the right to say what that URI stands for.
>
> OK. So, what DOES that URI stand for? How will you tell someone  
> what the referent is that you intend it to denote, so that they  
> know what to use it for? Now of course, you and I being smart human  
> native English speakers who are reasonably tech-savvy can look at  
> this and figure out that it is probably meant to refer to you. But  
> really, that does depend on us being this smart and savvy.

Well,  I put it in the Tabulator and I get out (among other stuff):

  Tim Berners-Lee
	Assistant		Amy van der Hiel
	HomePage		http://www.w3.org/People/Berners-Lee/
	Work		
		Address		
			City		Cambridge
			Country		USA
			PostalCode		02139
			Street		32 Vassar Street
			Street2		MIT CSAIL Room 32-G524
		Phone		tel:+1-617-253-5702
		Latitude		42.361860
		Longitude		-71.091840
	Organization		expandfetchWorld Wide Web Consortium

which to many people gives a fairly lear indication of what is  
identified.  And in fact for non-english speakers, there are words to  
the effect that "Sir Tim Berners-Lee is geboren in Londen in 1955.  
Hij wordt gezien als de bedenker en grondlegger van het World Wide  
Web (WWW), dat was geïnspireerd door HyperCard. Hij werkte hierin  
samen met de Belg Robert Cailliau. Als directeur van het World Wide  
Web Consortium houdt hij toezicht op de ontwikkeling van webtalen en - 
protocollen als HTML, XML, CSS en HTTP. Berners-Lee schreef ook de  
eerste webbrowser, net als het web World Wide Web genaamd, en de  
eerste webserver." and
Sir Timothy "Tim" John Berners-Lee, KBE (TimBL o TBL). Nacido el 8 de  
junio de 1955 en Londres Inglaterra, se licenció en Física en 1976 en  
el Queen's College de la Universidad de Oxford. Sus padres eran  
matemáticos. Trabajando como investigador en el Laboratorio Europeo  
de Física de Partículas (CERN) de Ginebra, concibió la idea de un  
proyecto de hipertexto global, que años más tarde se convertiría en  
la world wide web.""


> It isn't absolutely obvious: and there are many, many web pages out  
> there which I really have no idea what their owners would say they  
> denote.

(Web pages? Web pages are documents.  I wouldn't say they denote  
things.  Symbols, like URIs, denote.
The URI <http://www.w3.org/People/Berners-Lee/card#i> denotes me, and  
the URI <http://www.w3.org/People/Berners-Lee/card> denotes the web  
page: an RDF one, but a web page.  That web page describes mainly me  
but also to an extent other people and things.)



>> To use it for something else is an error.
>
> But surely if you make this ruling then it is up to you to tell me  
> enough about what it is supposed to be used for, so that I can know  
> when Im making an error. HOW??

Well,  do you want the human way of the machine way?
- The human way is that you are tempted to use it to represent my car  
but  you see the stuff above, and you realize that for example,  
people would be concerned about the weight property and so on.
- The machine way could be for example that you operate with an OWL  
system which include the belief that foaf:Person and dot:Car are  
distinct classes, which will flag an error.

>   And what about a URI that I own and wish it to denote, say, the  
> planet Venus, or my pet cat? What do I do, to attach the URI to my  
> intended referent for it?
>
>>>
>>> In my opinion to denote (or to identify) is a verb, something  
>>> that is done by the users of a symbol. After all, symbols (URI)  
>>> are not agents, they don't wake up and choose to denote this or  
>>> that.
>>
>> They have wonders which create them for a specific purpose.
>
> wonders/owners I presume.

yes

>
> But the key question to me is, how can they communicate the purpose  
> to the reader? How does one publish an intention? How does one  
> indicate a referent, other than by describing it? How much  
> description is enough?

Experience shows.  This is engineering.
That question is I suppose one agonized over by working groups all  
the time.
Fortunately, there are social systems not only for announcing that a  
UTI has been minted and describing what it denotes, but also for  
getting feedback from people who don't understand it, or whose  
machines are not able to process it. This feedback can lead to an  
adjustment of the information out there, publication of tutorials,  
and so on.



>
>>> Nor do I think denotation is an attribute or property of a  
>>> symbol, somehow built in or attached when the symbol is first  
>>> conceived. It is more like a dance. I use a symbol to denote  
>>> something expecting you to interpret it to denote the same thing.  
>>> And this coordination, this synchrony of interpretation by both  
>>> sender and receiver, is not always easy. It requires real effort  
>>> to sustain it. The minter of a URI cannot make it happen by  
>>> declaration, nor can a research group or a standards body just  
>>> decree it so.
>>
>> In many cases, the URI is defined by connection to already well- 
>> defined sets of things.  In other cases, such as the terms in the  
>> OWL ontology, there was a huge amount of effort and discussion  
>> involved, and the current term is supported by a lot of ongoing  
>> tutorials and so on.  No one said it was easy.  But it is a  
>> different architecture from dance associated with natural language  
>> words.
>
> The huge effort was for defining the meanings of the OWL reserved  
> vocabulary, and that is indeed about as defined as a vocabulary can  
> get. But if we just take some OWL ontology and ask how well it  
> constrains the meanings of the new URIs that occur in it, this is  
> *very* much like the word dance that John refers to. In fact in all  
> essentials it seems to me to be pretty much the same game. I  
> publish (say) some stuff which I intend to mean something, you read  
> (hear) it and get some insight into my meaning. You draw some  
> conclusions and if you send (tell) them to me I can check to see if  
> I agree and if not try to send (say) some more to you to make your  
> grasp of my intentions more firm.

Yes, of course the game happens.  But for example when I download my  
OFX bank statements,
then my computer processes them.  Millions of people do this.  Very  
very few of them worry about who
did the dance, or do the dance themselves.  Actually, some people  
from banks, Microsoft and Inituit etc did the dance.  This is the  
"total cost of ontologies" argument.


>
> It HAS to be similar, barring machine telepathy. There really isn't  
> anything that either people or machines can do much beyond send  
> symbols to one another: and symbols carry meaning only imperfectly,  
> with inherent ambiguity.

Yes. In theory, there is always a very small possibility that I  
completely misunderstand the way you use a word, say "car", and a  
moderate probability that in some small very rare corner case we  
haven't come across yet, we in pedantic mode would disagree about its  
meaning.

The extent to which I can behave, and build systems, as though in  
fact the terms had well-defied meanings depends on the amount of  
dancing which has been done.   As the dance is done, the structures  
in my brain and those in yours, while never identical, become very  
similar, specifically in that they develop an very strong association  
between a class of real-world object (car) or concept  
(TransitiveProperty).
Philosophy studies the dance.  (Philosophy has ion the past been  
distracted by a concern that you can't measure the brain's structure,  
and you can't measure an external TranstiveProperty object.  The fact  
htat philsophers have found this difficult doesn't stop the fact that  
it happens, and now we have fMRI machines we are even relieving some  
of this angst. But I digress)


The important thing is that as the dance is done, the probability of  
major disagreement, and the degree of pedantic disagreement,   
decrease very dramatically, to become negligible for engineering  
purposes.


>>
>> It is different by design.  The semantic web is an engineered  
>> system, not an observation of nature.
>
> But it is a real system, and so it has to obey laws of nature. And  
> there are laws of meaning as well as of physics.

You bring up physics. Indeed.  As an engineer, I design my coffee mug  
to stay in one place: with no wheels. Does it?   It is a real system,  
and  so it has to obey laws of nature.  Physics tells as that at any  
time, there is a finite possibility that any object might just be  
measured to be in a different place, such as a foot to the right and  
no longer around my coffee.  In fact if I study the construction of a  
coffee mug from particles, all kinds of questions arise, as the first  
few particles are very difficult to manage.  I can't even build a  
tool which will tell me where the stupid electron is, without my  
being completely unaware of its momentum.   Given that I can't  
actually claim to have put an electron and proton together with any  
degree of accuracy, how can I claim to be able to build a mug which  
will stay in one place.  Well, it turns out that as the number of  
particles becomes larger, these effects, while still true, just  
become ignorable for engineering purposes.

The analogy is limited, of course.

>>> The reason this matters is that since it requires this effort to  
>>> create a denotation/identification in the first place, it is far  
>>> more sensible, to me at least, to expect that the final  
>>> disambiguation of a symbol be accomplished in the same way, by  
>>> coordinated effort of the parties using the symbol, not by  
>>> declaration of the W3C specifications that all URIs be absolutely  
>>> unambiguous.
>>> This seems to me to be, as my grandfather used to say, a vain task.
>>
>> Your grandfather would perhaps have suggested that an attempt to  
>> define the meaning of common words, as the Académie Française is  
>> set up to do were a 'vain task'.   Many would agree.  But given  
>> that his water came to him though pipes connected, possibly, by  
>> half-inch British Standard pipe-thread connections, and he rode on  
>> rails set a certain distance apart by some committee, and his TV  
>> came for better or worse in 525 or 625 lines as decided by other  
>> committees, he may have respected that the creation of standards  
>> is a very valuable function, and an essential to progress.
>>
>> When people meet to define W3C specifications they are not doing  
>> it out of vanity.   They are performing coordinated effort of the  
>> parties who would like to be able to use the symbol.  They are, in  
>> general, users and representatives of users of the symbol.   They  
>> come together to allow those who follow them to use it. They often  
>> work long hours, receiving inadequate recognition for either  
>> products shipped or papers published, the conventional metrics of  
>> performance, so I would not call it vanity.
>
> The point surely is that URIs used to refer (not as in HTTP, but as  
> in OWL) do *not* have a standardized meaning. Standards are  
> certainly a chore to create, but they only go so far. OWL defines  
> the meanings of the OWL namespace, but it does not define the  
> meanings of the FOAF vocabulary, or the URIrefs used in, say,  
> ontologies published by the NIH or by JPL.

Ah, so you accept that the OWL working group has effectively given  
meanings to the the terms in the OWL namespace, but you don't think  
that the FOAF friends gave meaning to the FOAF namespace, or the NCBI  
to its ontologies? How curious.  OWL does indeed only go so far.   
FOAF and OFX and so on  go  bit further, but also  only so far.  They  
all create new terms which, modulo arguments afterward an so on,  
become with time an increasingly stable foundation for communication  
between parties.


> The only way those meanings can be specified is by writing  
> ontologies: and finite ontologies do not - cannot possibly - nail  
> down referents *uniquely*. No amount   of authority-delegating or  
> standard-setting is going to change this basic fact.

Fortunately, the trains continue to run, and bank statements continue  
to generate graphs and tax forms, more and more people say they  
foaf:knows each other, despite the fact that none of them or the  
relationships have been defined really completely precisely to the  
complete mutual understanding of all parties.

This seems to me to be a very important bridge between philosophy of  
microscopic linguistic interactions of agents, and the large scale  
world of communities with common terms which are 'good enough for  
government work'.  I suppose I am surprised it isn't in the textbooks.

Tim

> Pat
>
>
>
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Received on Wednesday, 13 June 2007 15:16:08 UTC

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