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Re: Terminology Question concerning Web Architecture and Linked Data

From: Alan Ruttenberg <alanruttenberg@gmail.com>
Date: Sun, 22 Jul 2007 21:16:40 -0400
Message-Id: <BDA3F7EF-3AC9-4103-8598-E16C2E5F02D1@gmail.com>
Cc: "SW-forum Web" <semantic-web@w3.org>, "Linking Open Data" <linking-open-data@simile.mit.edu>, "Jonathan A Rees" <jar@mumble.net>, <www-tag@w3.org>
To: Chris Bizer <chris@bizer.de>

Hi Chris,

While you outline an interesting problem, it doesn't address the  
question I asked. Specifically, you said:

On Jul 20, 2007, at 9:02 AM, Chris Bizer wrote:
> we argue in section 1.1 of our Linked Data tutorial (http:// 
> sites.wiwiss.fu-berlin.de/suhl/bizer/pub/LinkedDataTutorial/ 
> #aliases) that URI aliases provide an important social function to  
> the Web as they are dereferenced to different descriptions of the  
> same non-information resource and thus allow different views and  
> opinions to be expressed.
>
> Which is an interesting conclusion as it conflicts with the AWWW  
> view that URI aliases are harmful.
> See http://www.w3.org/TR/webarch/#uri-aliases

In other words, these aliases are not simply a necessary evil, but a  
positive good. This was the claim I was (and am still) testing.

In particular, your advise is that when providers know of the  
existence of alternate URIs, they note this with owl:sameAs,  
implicitly recommending this mechanism rather than the alternative of  
simply using an already minted URI that denotes the same thing.

To my mind it might make more sense to do the latter, and it is to  
this that the webarch reference you note speaks to.

So you have two novel claims:

1) It is better to mint your own URI than to use one that you know to  
identify the same resource.
2) It is better to attach "different views and opinions" about a  
known resource to a newly minted URI that you state is owl:sameAs  
some other rather than using an alternative mechanism for doing so,  
one of which might be the one I suggested.

Do I read you wrong?

-Alan


On Jul 22, 2007, at 4:29 PM, Chris Bizer wrote:

> Hi Alan,
>
>> Thanks for the more detailed information. While I agree with the  
>> need  to be able to have a mechanism for making statements about  
>> URIs that  one doesn't mint, such as http://www.w3.org/People/  
>> Berners-Lee/  card#i, what I don't follow in your discussion is  
>> why such additional  statements need to be attached to an alias  
>> (in the sameAs sense) of  the original URI. It would seem worth  
>> justifying this in the light of  the associated costs of such aliases
>>
>> - The lower likelihood of successful "joins" in queries if a) Not  
>> all "sameAs"s are available to an agent or b) The agent's reasoner  
>> isn't capable of correctly handling sameAs
>> - The uncertain semantics of sameAs when taken out of the context  
>> of  the OWL specification.
>>
>> For instance, why not have e.g. dbpedia only name *resources*  
>> which  are understood as "community statements about" some  
>> subject, in which statements about tbl would use his designated  
>> name for himself?
>>
>
> Yes, in a perfect world you are right, but unfortunately, we are  
> not living in a perfect world.
>
> DBpedia is a good example for this. We are assigning URIs to  
> 1,600,000 resources and we don't have a clue which URIs we assign  
> to some town, molecules, flowers or planets. We even don't know if  
> we assign URIs to flowers at all, before we search within our  
> dataset for flowers.
>
> We do this because we want to create a useful open dataset in the  
> short term. If we would wait until there is community agreement in  
> each domain that DBpedia covers about a naming schema or wait until  
> each of the described resources has assigned a URI to itself, we  
> won't get anywhere. If there would be community agreement about  
> naming schemata (which there is not and I also do not expect such  
> agreement to evolve in the mid-future), the next problem would be  
> to bring some complicated infrastructure into place that allows  
> applications like DBpedia to find out that http://www.w3.org/People/ 
> Berners-Lee/card#i is only URI that should be used to refer to Tim  
> (think about stuff like URI SPAM and all the trust mechanism such  
> an infrastructure would need).
>
> So, I think that the approach of assuming that single URIs for  
> identifying real-world resources will evolve does not scale for  
> practical reasons.
>
> Evidence for this opinion can be found in the Linking Open Data  
> project (http://esw.w3.org/topic/SweoIG/TaskForces/ 
> CommunityProjects/LinkingOpenData) where most datasources are  
> backed by large legacy databases and it is unrealistic to require  
> publishers to find out the only acceptable URI for each of their  
> 100 000 data items.
>
> The project is aiming at having hundreds of billions RDF triples  
> online in the mid-term. Think of data souces like Freebase (http:// 
> www.freebase.com/), the Open Library (http://demo.openlibrary.org/)  
> or all public US government data (http://www.cs.umd.edu/class/ 
> spring2006/cmsc838s/data_repositories/repository_us.html).
>
> In such situations, I think it is more realistic from the practical  
> point of view to use a two step process:
>
> 1. Allow each data provider to assign his own URIs to resources  
> (not much effort for him, just dump his database as Linked Data).
> 2. Use some equivalence mining algorithms afterwards to find out  
> which URIs talk about the same things.
>
> We do a lot of such equivalence mining in the Linking Open Data  
> project and it works fine (good enough).
> See: http://sites.wiwiss.fu-berlin.de/suhl/bizer/pub/ 
> LinkedDataTutorial/#autogenerateLinks and
> http://esw.w3.org/topic/TaskForces/CommunityProjects/ 
> LinkingOpenData/EquivalenceMining
>
> I agree with you that this approach has a "lower likelihood of  
> successful "joins"", but I rather prefer to data mine useful  
> information out of a pile of junk than to wait until there is  
> community agreement about ontologies and naming schemata.
>
> Note, that this approach is also taken by Google Base and these  
> guys are already rather successful with it.
>
> I'm also not too concerned about the "agents reasoner not being  
> capable of correctly handling sameAs". I expect that agents and  
> search engine will implement reasoners for specific sets of  
> predicates (and owl:sameAs is very likely to be in this set). I'm  
> sceptical about general RDF-S/OWL reasoners, because it will take a  
> while until they are capable to handle hundreds of billions of  
> triples and this is the amount of data that we need to in order to  
> relevant in the light of Web 2.0.
>
> Cheers
>
> Chris
>
>
>> -Alan
>>
>
> On Jul 20, 2007, at 9:02 AM, Chris Bizer wrote:
>
>> Hi Alan,
>>
>>> However, I am curious to know what you were asking, so if you  
>>> do,  I will be appreciative.
>>
>> My question was aiming more into the direction of how AWWW and OWL  
>> terminology plays together.
>>
>> owl:sameAs if defined as "The built-in OWL property owl:sameAs   
>> links an individual to an individual. Such an owl:sameAs  
>> statement  indicates that two URI references actually refer to the  
>> same thing:  the individuals have the same "identity" (http:// 
>> www.w3.org/TR/owl- ref/#sameAs-def)
>>
>> There was a long discussion and a lot of confusion on the SemWeb   
>> list about two weeks ago whether owl:sameAs is the right  
>> predicate  that should be used to indicate that two URIs refer to  
>> the same  "thing". With "thing" being a OWL term that does not  
>> exist in AWWW  terminology.
>>
>> So, if the anwer to my first question would have been that the   
>> different URIs for Tim refer to different resources, there would   
>> have been a problem with "refering to the same thing". But as  
>> Dan's  answer to my first question indicated that the different  
>> URIs refer  to the same non-information resource, meaning that  
>> they are URI  aliases, there is no problem and I see the issue as  
>> being closed.
>>
>> Building on this, we argue in section 1.1 of our Linked Data   
>> tutorial (http://sites.wiwiss.fu-berlin.de/suhl/bizer/pub/  
>> LinkedDataTutorial/#aliases) that URI aliases provide an  
>> important  social function to the Web as they are dereferenced to  
>> different  descriptions of the same non-information resource and  
>> thus allow  different views and opinions to be expressed.
>>
>> Which is an interesting conclusion as it conflicts with the AWWW   
>> view that URI aliases are harmful.
>> See http://www.w3.org/TR/webarch/#uri-aliases
>>
>> Cheers
>>
>> Chris
>>
>>
>> --
>> Chris Bizer
>> Freie Universitšt Berlin
>> Phone: +49 30 838 54057
>> Mail: chris@bizer.de
>> Web: www.bizer.de
>>
>> ----- Original Message ----- From: "Alan Ruttenberg"  
>> <alanruttenberg@gmail.com>
>> To: "Chris Bizer" <chris@bizer.de>
>> Cc: "Dan Connolly" <connolly@w3.org>; <www-tag@w3.org>; "SW-forum   
>> Web" <semantic-web@w3.org>; "Linking Open Data" <linking-open-  
>> data@simile.mit.edu>; "Jonathan A Rees" <jar@mumble.net>
>> Sent: Friday, July 20, 2007 2:28 PM
>> Subject: Re: Terminology Question concerning Web Architecture and   
>> Linked Data
>>
>>
>> Hi Chris,
>>
>> Your assessment is perfectly reasonable. I was thrown off by the
>> question you initially asked:
>>
>>> Question 3: Depending on the answer to question 1, is it correct   
>>> to use owl:sameAs [6] to state that http://www.w3.org/People/   
>>> Berners-Lee/ card#i and http://dbpedia.org/resource/Tim_Berners-  
>>> Lee refer to the same thing as it is done in Tim's profile.
>>
>> Given that you didn't intend the sense of "correct" that I thought
>> (recall that I was guessing, from context, which sense of correct you
>> meant in your question), which sense of "correct" did you mean? Or to
>> phrase it another way, if one were to answer the question "no", what
>> sort of evidence would you accept to support that answer.
>>
>> This isn't a matter of philosophy, it's a matter of communication. I
>> really don't know what you are asking. Another way to accomplish the
>> communication would be to rephrase the question without using the
>> word "correct".
>>
>> I don't mean to suggest you are obligated to clarify this for me.
>> However, I am curious to know what you were asking, so if you do, I
>> will be appreciative.
>>
>> -Alan
>>
>>
>>
>> On Jul 20, 2007, at 3:55 AM, Chris Bizer wrote:
>>
>>> Hi Alan,
>>>
>>> I'm not a philosopher, but I have the feeling that the concept   
>>> "correct" in a sence of matching reality does not really apply  
>>> to  the Semantic Web setting.
>>>
>>> We are talking about machines that are supposed to process data   
>>> from different sources. There is no such thing as "reality" for  
>>> a  machine. For the machine there is only data! (or knowledge if  
>>> you  prefer this term)
>>>
>>> Therefore the question for the machine is: Should it trust a   
>>> specific piece of data or not? Or more precisely how can it  
>>> assess  the quality of the data to a point where it matches the  
>>> quality  requirements of the user (human).
>>>
>>> There are lots of different heuristics that a machine can apply  
>>> to assess information quality, including content-based, context-  
>>> based, rating-based heuristics.
>>>
>>> For more details than you ever wanted to hear, please refer to  
>>> my  PhD thesis titeld "Quality-driven Information Filtering in  
>>> the  Context of Web-based Information System" http:// 
>>> sites.wiwiss.fu- berlin.de/suhl/bizer/pub/DisertationChrisBizer.pdf
>>>
>>> Cheers
>>>
>>> Chris
>>>
>>> --
>>> Chris Bizer
>>> Freie Universitšt Berlin
>>> +49 30 838 54057
>>> chris@bizer.de
>>> www.bizer.de
>>> ----- Original Message ----- From: "Alan Ruttenberg"  
>>> <alanruttenberg@gmail.com>
>>> To: "Dan Connolly" <connolly@w3.org>
>>> Cc: "Chris Bizer" <chris@bizer.de>; <www-tag@w3.org>; "SW-forum   
>>> Web" <semantic-web@w3.org>; "Linking Open Data" <linking-open-  
>>> data@simile.mit.edu>; "Jonathan A Rees" <jar@mumble.net>
>>> Sent: Friday, July 20, 2007 4:52 AM
>>> Subject: Re: Terminology Question concerning Web Architecture  
>>> and  Linked Data
>>>
>>>
>>>> On Jul 10, 2007, at 1:08 PM, Dan Connolly wrote:
>>>>> On Sat, 2007-07-07 at 14:43 +0200, Chris Bizer wrote:
>>>>>
>>>>>> Question 3: Depending on the answer to question 1, is it    
>>>>>> correct to use
>>>>>> owl:sameAs [6] to state that http://www.w3.org/People/ 
>>>>>> Berners-  Lee/ card#i and
>>>>>> http://dbpedia.org/resource/Tim_Berners-Lee refer to the same   
>>>>>> thing as it is
>>>>>> done in Tim's profile.
>>>>>
>>>>> Yes...
>>>>>
>>>>> That's sort of a circular question. It's correct because Tim    
>>>>> says it's correct, and he owns that name.
>>>>
>>>> That's not the usual sense of "correct". In this context, I   
>>>> believe that the wordnet sense of "correct" that is intended is
>>>> "free from error; especially conforming to fact or truth"
>>>>
>>>> Or Wikipedia: "In everyday use, the correctness of a statement  
>>>> is determined by whether or not it matches reality. People can  
>>>> think  a statement is correct and be wrong."
>>>>
>>>> If I had a profile that said, in effect, that I was president  
>>>> of  the United States, then that would be incorrect regardless  
>>>> of  whether I owned the name (I am taking the "owned name" that  
>>>> you  are referring  to to be http://www.w3.org/People/Berners- 
>>>> Lee/  card#i since that's the only name in the vicinity that Tim  
>>>> could  correctly claim to be owned by him).
>>>>
>>>> If I'm using the wrong sense of "correct", perhaps you could   
>>>> provide me a definition of "correct" by which I could  
>>>> understand  your claim.
>>>>
>>>> Regards,
>>>>
>>>> -Alan
>>>
>>
>
>
Received on Monday, 23 July 2007 01:16:50 GMT

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