W3C home > Mailing lists > Public > semantic-web@w3.org > January 2008

RE: Cool URIs, the Semantic Web and Everything

From: <tim.glover@bt.com>
Date: Wed, 2 Jan 2008 10:39:35 -0000
Message-ID: <AEF15555D64C494CA393778177A3A17102B83317@E03MVC1-UKBR.domain1.systemhost.net>
To: <richard@cyganiak.de>
Cc: <michael.hausenblas@joanneum.at>, <semantic-web@w3.org>


Richard,

Happy 2008. I agree that calling people mad is very poor - I did not
mean to imply that any individual was mad, most particularly not you, or
anyone else on this thread, and I apologise unreservedly if I caused
offence.  

It seems to me that using URIs to refer to unique resources is analogous
to using database primary keys to refer to unique records - to break
this convention is an error which invalidates the specs and will lead to
unpredictable results. I think this is your view too - and if you still
think I am mistaken, I am inclined to think that you are right and I am
wrong. I bow to your expertise in this. 

My point was a different one, and relates to how URIs are used to refer
to real world entities, such as the person "Michael". This touches on
another question by Henry Story, who asks what is the difference between
machines and people. 

My view is that software systems are *models* of the real world, not
replicas. Software is useful to the extent that it is related to the
real world, and useless to the extent that it is not.  The "mad" idea is
not that we can use a unique key to refer to a software data item, but
that there must be a unique interpretation of this key in the real
world. (Eg, As many, many people have noted in the past, the name
"Michael" is unambiguous *within the context of this discussion*, and
that is good enough.)

I know this is an old, old argument, and I do NOT want to start a whole
new weary thread on the subject, I am just keeping the idea alive, in
the spirit of a christmas quiz :)

Respectfully yours,

Tim. 

 

-----Original Message-----
From: Richard Cyganiak [mailto:richard@cyganiak.de] 
Sent: 01 January 2008 15:35
To: Glover,T,Tim,CXR3 R
Cc: michael.hausenblas@joanneum.at; semantic-web@w3.org
Subject: Re: Cool URIs, the Semantic Web and Everything

Tim,

Happy 2008, first of all.

On 31 Dec 2007, at 13:14, <tim.glover@bt.com> <tim.glover@bt.com> wrote:
> QIIa. What does it mean? It depends on the context. In a software 
> context this string of letters could represent a URI, a password, an 
> encrypted sentence, a long integer... In the context of *semantic web
> software* its meaning is given by the specs, and I guess Richards 
> answer is authoritative. But it sounds as if there are several 
> software specs that could be applied - I think your option 5 comes 
> closest.

(Michael's option 5 was: "Depends on who looks at it: A Web UA 'sees'  
a XHTML fragment, a SW agent a thing of type foaf:Person")

Tim, you are right to some extent. Because of the way Michael has
configured his URI, there are several specs that could be applied. The
URI spec says one thing ("It's a part of a document"), the RDFa spec
says another thing ("It's a person"), and that appears to be a
contradiction.

Now, there is a school of thought that considers this situation to be
harmful. According to this school of thought, URI owners should never
configure their URIs in a way that results in contradictory
interpretation when different specs are applied. Michael, as the URI
owner, has made a mistake in configuring his URI, and he should fix it.
The principle is best stated in AWWW [1]:

    Constraint: URIs Identify a Single Resource.
    Assign distinct URIs to distinct resources.

Proponents of this practice think that following this practice leads to
desirable properties in the system as a whole. They think that the Web
works best when everyone follows this practice.

> Q II. What does it identify? Only a human interpreter can tell you.  
> And
> the law that says it can only possibly refer to one thing is mad and 
> unenforceable.

Calling people mad doesn't help. Maybe you can clarify your position a
little bit? As you see above, there is no law, but there is a certain
practice, and there are people who strongly encourage URI owners to
follow that practice.

Now the question is where do you disagree? Do you think that

a) The practice is indeed good and would indeed lead to desirable
properties, if only URI owners would follow it; but you don't believe
that URI owners will ever follow it, or

b) The practice does not lead to desirable properties, and therefore
it's a waste of time to ask URI owners to follow it, or

c) The practice is actually harmful or misguided, and there are
situations where we should clearly encourage URI owners to do as Michael
did, even though this leads to apparent contradictions when different
specs are applied, or

d) You reject the idea of the Web as "a system as a whole" that can be
improved by applying practices like the above?

Cheers,
Richard

[1] http://www.w3.org/TR/webarch/#id-resources


>
>
> Tim.
>
>
>
>
> Q.I: What is http://sw-app.org/mic.xhtml#i?
>
> 1. A URI
> 2. A URL
> 3. A foaf:Person
> 4. Michael Hausenblas
> 6. An XHTML fragment
>
>
> Q.II:  What does http://sw-app.org/mic.xhtml#i identfiy?
>
> 1. A foaf:Person
> 2. Michael Hausenblas
> 4. An XHTML fragment
> 5. Depends on who looks at it: A Web UA 'sees' a XHTML fragment,
>   a SW agent a thing of type foaf:Person 6. Dunno until I do an HTTP 
> GET
>
>
> Cheers,
> 	Michael
>
> ----------------------------------------------------------
> Michael Hausenblas, MSc.
> Institute of Information Systems & Information Management  JOANNEUM 
> RESEARCH Forschungsgesellschaft mbH  Steyrergasse 17, A-8010 Graz, 
> AUSTRIA
> ----------------------------------------------------------
>
>> -----Original Message-----
>> From: Richard Cyganiak [mailto:richard@cyganiak.de]
>> Sent: Friday, December 21, 2007 5:26 PM
>> To: Hausenblas, Michael
>> Cc: Leo Sauermann; semantic-web@w3.org; Leo Sauermann
>> Subject: Re: Cool URIs, the Semantic Web and Everything
>>
>> Michael,
>>
>> On 21 Dec 2007, at 08:23, Hausenblas, Michael wrote:
>>> In Cool URIs you are
>>> referring to a certain
>>> setup ('deployment scenarios in which the RDF data and the
>> HTML data
>>> is served separately').
>>> Also the figure right before section 3.1 suggests that there is an 
>>> explicit RDF document and an HTML document, each with a
>> distinct URL.
>>> As you know, this is not the case with RDFa.
>>
>> Would changing the sentence
>>
>> "In those cases [RDFa, microformats and GRDDL] the RDF data is 
>> extracted from the returned HTML document."
>>
>> to
>>
>> "In those cases, the RDF data is extracted from the HTML document and

>> no separate RDF document is needed."
>>
>> address your complaint?
>>
>> The rest of the document's narrative is consistent with use of RDFa, 
>> as far as I can tell.
>>
>> Best,
>> Richard
>>
>>
>>>
>>>
>>> So, that is were my confusion stems from. I know that due to time 
>>> constraints you decided that this is the way it is. It
>> would still be
>>> nice to learn why the figure right before section 3.1
>> (sorry, no label
>>> available) 'shows the desired relationships between a
>> resource and its
>>> describing documents'.
>>>
>>> Cheers,
>>> 	Michael
>>>
>>> [1]
>> http://lists.w3.org/Archives/Public/semantic-web/2007Dec/0121.html
>>>
>>> ----------------------------------------------------------
>>> Michael Hausenblas, MSc.
>>> Institute of Information Systems & Information Management JOANNEUM 
>>> RESEARCH Forschungsgesellschaft mbH
>>>
>>> http://www.joanneum.at/iis/
>>> ----------------------------------------------------------
>>>
>>>
>>>> -----Original Message-----
>>>> From: Leo Sauermann [mailto:sauermann@dfki.uni-kl.de]
>>>> Sent: Thursday, December 20, 2007 12:36 PM
>>>> To: Hausenblas, Michael
>>>> Cc: semantic-web@w3.org; Leo Sauermann
>>>> Subject: Re: Cool URIs, the Semantic Web and Everything
>>>>
>>>> Hausenblas, Michael schrieb:
>>>>
>>>> 	Leo,
>>>> 	
>>>> 	Thanks for your explanation. I remain not totally convinced :)
>>>> 	
>>>>
>>>> good, then give a practical example (using concrete RDFa
>> code) where
>>>> you think some work needs to be done and provide a
>> suggestion how to
>>>> solve it. That you are not convinced may be caused by
>> various reasons
>>>> we don't know about, shine light on them.
>>>>
>>>>
>>>>
>>>> 	
>>>> 	So, *if* we agree on what you said, IMHO we should
>>>> 	reconsider the following paragraph in 'Cool URIs' [1]:
>>>> 	
>>>> 	'The solutions described in the following apply to deployment 
>>>> scenarios
>>>> 	in which the RDF data and the HTML data is served
>> separately, such
>>>> as a
>>>> 	standalone RDF/XML document
>>>> 	along with an HTML document. The metadata can also be
>> embedded in
>>>> HTML,
>>>> 	using technologies such as
>>>> 	RDFa [RDFa Primer], microformats and other documents to
>> which the
>>>> GRDDL
>>>> 	[GRDDL] mechanisms can be applied.
>>>> 	In those cases the RDF data is extracted from the returned HTML
>>>> 	document.'
>>>> 	
>>>>
>>>> I see no reason for changes until you exactly specify where this 
>>>> paragraph contradicts http-range-14 or other TAG
>> resolutions or W3C
>>>> recommendations.
>>>>
>>>> the point is that RDF/XML, N3, RDFa and GRDDL are
>> mimetypes encoding
>>>> RDF triples while URIs are something used inside these RDF
>> triples,
>>>> so at the beginning both are completly different and do not affect 
>>>> each other.
>>>>
>>>> "Cool uris" is about URIs and not about RDF serialization.
>>>>
>>>> best
>>>> Leo
>>>>
>>>>
>>>>
>>>> 	
>>>> 	Still unsure if this is just the tip of the iceberg ...
>>>> 	
>>>>
>>>> 	
>>>> 	Cheers,
>>>> 		Michael
>>>> 	
>>>> 	[1] http://www.w3.org/TR/2007/WD-cooluris-20071217/#solutions
>>>> 	
>>>> 	----------------------------------------------------------
>>>> 	 Michael Hausenblas, MSc.
>>>> 	 Institute of Information Systems & Information Management
>>>> 	 JOANNEUM RESEARCH Forschungsgesellschaft mbH
>>>> 	
>>>> 	 http://www.joanneum.at/iis/
>>>> 	----------------------------------------------------------
>>>> 	
>>>> 	
>>>> 	
>>>>
>>>> 		-----Original Message-----
>>>> 		From: Leo Sauermann [mailto:sauermann@dfki.uni-kl.de]
>>>> 		Sent: Thursday, December 20, 2007 3:43 AM
>>>> 		To: Hausenblas, Michael
>>>> 		Cc: semantic-web@w3.org; Leo Sauermann
>>>> 		Subject: Re: Cool URIs, the Semantic Web and Everything
>>>> 		
>>>> 		Hi Michael, RDFa people,
>>>> 		
>>>> 		The question is if httpRange-14 [2] is valid in
>> the case of
>>>> XHTML+RDFa.
>>>> 		
>>>> 		The answer is that httpRange-14 is to
>> distinguish URIs for
>>>> information
>>>> 		resources ("web documents") from real-world
>> objects (the person
>>>> 		"Alice"). As such, it is a recommendation on URIs.
>>>> 		
>>>> 		RDFa is an encoding of RDF, and typically an
>> RDFa document has two
>>>> 		relations to URIs:
>>>> 		a) the URI of the RDFa document (=the
>> information resource where I
>>>> can
>>>> 		download the RDFa document)
>>>> 		b) the URIs used as subjects, predicates,
>> objects inside RDF
>>>> 		statements
>>>> 		written inside RDFa documents
>>>> 		
>>>> 		a) is usually a http-200 uri, and a) is an
>> information resource (=
>>>> a
>>>> 		document).
>>>> 		In the rdf statemetns written inside  A, you
>> would use both URIs
>>>> for
>>>> 		real-world objects and information resources.
>>>> 		example (I don't know  rdfa syntax by heart
>> now, assume this is
>>>> rdfa):
>>>> 		
>>>> 		document at www.example.com/homepage/aboutAlice
>>>> 		<html>
>>>> 		<p
>>>> rdf:about="http://www.example.com/identifiers/alice#this"
>>>> <http://www.example.com/identifiers/alice#this> >
>>>> 		 rdf:type foaf:Person.
>>>> 		</p>
>>>> 		<p
>>>> rdf:about="http://www.example.com/moreidentifiersusing303/bob"
>>>> <http://www.example.com/moreidentifiersusing303/bob> >
>>>> 		rdf:type foaf:Person
>>>> 		</p>
>>>> 		</html>
>>>> 		
>>>> 		assuming this would be valid RDFa, the URI
>> .../aboutAlice is a
>>>> 		http-return-200 informaiton resource
>>>> 		.../alice#this is a real-world object as it is
>> not a document (as I
>>>> 		understand timbl on that)
>>>> 		...303/bob is not intuitively distinguishable -
>> if you ignore the
>>>> 		rdf:type relation you don't know what it is. So
>> for this uri you do
>>>> a
>>>> 		HTTP get and the server would return a 303
>> redirect as described in
>>>> 		"cool uris".
>>>> 		once oyu did the 303, you knowthat ....303/bob
>> is a real world
>>>> object.
>>>> 		
>>>> 		so RDFa and 303'/httprange14 are
>>>> recommendations caring about
>>>> 		different
>>>> 		angles, 303 is only concerned about URIs, RDFa
>> about an RDF
>>>> 		serialization. Technically they don't interfere.
>>>> 		
>>>> 		If I would use RDFa much and would like cool
>> uris, I would go for
>>>> 		#-uris, they are simple to use and easy to
>> embed in RDFa.
>>>> 		but as shown above, you can use any URI you
>> want inside rdfa.
>>>> 		
>>>> 		best
>>>> 		Leo
>>>> 		
>>>> 		
>>>> 		Hausenblas, Michael schrieb:
>>>> 		
>>>>
>>>> 			===
>>>> 			Disclaimer: Michael, with his
>>>> RDFa-Task-Force-member hat off ;)
>>>> 			===
>>>> 			
>>>> 			As I gathered "Cool URIs for the Semantic Web"
> is a Working
>>>> 			
>>>>
>>>> 		Draft, now.
>>>> 		
>>>>
>>>> 			Congrats to Leo and his team, great job!
>>>> 			
>>>> 			The following might sound like a naive
>> question - and I might
>>>> 			have missed something :) - but: Is TAG
>> finding httpRange-14 [2]
>>>> 			equally valid in the case of XHTML+RDFa?
>>>> 			
>>>> 			I've put together some initial thoughts
>> at the ESWiki [3]
>>>> 			- any comments welcome!
>>>> 			
>>>> 			Cheers,
>>>> 				Michael
>>>> 			
>>>> 			[1]
>>>> 			
>>>>
>>>> 		
>>>> http://lists.w3.org/Archives/Public/public-swd-wg/2007Dec/0103.html
>>>> 		
>>>>
>>>> 			[2]
>>>> http://www.w3.org/2001/tag/issues.html#httpRange-14
>>>> 			[3] http://esw.w3.org/topic/RDFa_vs_RDFXML
>>>> 			
>>>> 			
>>>> ----------------------------------------------------------
>>>> 			 Michael Hausenblas, MSc.
>>>> 			 Institute of Information Systems &
>> Information Management
>>>> 			 JOANNEUM RESEARCH Forschungsgesellschaft mbH
>>>> 			 Steyrergasse 17, A-8010 Graz, AUSTRIA
>>>> 			
>>>> 			 <office>
>>>> 			    phone: +43-316-876-1193 (fax:-1191)
>>>> 			   e-mail: michael.hausenblas@joanneum.at
>>>> 			      web: http://www.joanneum.at/iis/
>>>> 			
>>>> 			 <private>
>>>> 			   mobile: +43-660-7621761
>>>> 			      web: http://www.sw-app.org/
>>>> 			
>>>> ----------------------------------------------------------
>>>> 			
>>>> 			
>>>> 			
>>>>
>>>> 		
>>>> 		
>>>>
>>>> 	
>>>> 	
>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>
>
>
Received on Wednesday, 2 January 2008 10:39:49 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 21:45:20 GMT