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Re: Terminology Question concerning Web Architecture and Linked Data

From: Chris Bizer <chris@bizer.de>
Date: Mon, 23 Jul 2007 09:23:26 +0200
Message-ID: <003101c7ccfa$5cf3f290$c4e84d57@named4gc1asnuj>
To: "Alan Ruttenberg" <alanruttenberg@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>


Hi Alan,

very fruitful discussion. Thanks for challenging me on this point :-)

> 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.

I basically see four arguments in favour of my point:

1. Practicability: There is no commonly accepted infrastructure in place 
that allows applications to find out the single URI that should be used by 
everybody to identify a resource. There are lots of real-world object and 
abstract concepts that do not have URIs yet, so you have to mint URIs for 
them yourself anyway. Also as Christopher Brewster pointed out yesterday, 
all approaches that assumed using single identifiers have failed throughout 
history so far.
2. Provenance Tracking: If you mint your own URIs you can back them up with 
RDF descriptions, which makes it easy to track who said what on the Semantic 
Web, as there is only one authoritative information provider for each URI.
3. Discovery: When you know that two URIs refer to the same non-information 
resource, it is extremely easy and does not require any new technical 
infrastructure to retrieve information about this resource from the Web: 
Just dereference both URIs.
4. Information Quality: Information providers will not set owl:sameAs links 
to minor quality information provided by somebody else about the same 
non-information resource. Therefore setting a owl:sameAs link implies a 
quality judgement and a client can use these judgements to assess 
information quality using an algorithm like PageRank.

I also do not say that you should always mint your own URIs. Note that we 
also have an example where somebody reuses an existing URI and provides 
non-authoritative information about a resource within our Linked Data 
tutorial 
(http://sites.wiwiss.fu-berlin.de/suhl/bizer/pub/LinkedDataTutorial/#deref).

I'm not also completely clear about which approach is better in which 
situations. This would be something very interesting to discuss here on the 
list.

I just say that there situations where minting your own URIs and 
interlinking them later with automated algorithms is more practical. At 
least it is more practical in the situation we are facing in the Linking 
Open Data project.

As we should aim at deploying the Semantic Web/Web of Data now, I also think 
that we should not wait for future name discovery infrastructures, community 
agreement about naming schemata or the like, but use an approach that works 
now.

> rather than using an alternative mechanism for doing so,  one of which 
> might be the one I suggested.

Alan sorry, which mechanism did you suggest?

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: "Chris Bizer" <chris@bizer.de>
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>
Sent: Monday, July 23, 2007 3:16 AM
Subject: Re: Terminology Question concerning Web Architecture and Linked 
Data


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 07:23:42 GMT

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