- From: Chris Bizer <chris@bizer.de>
- Date: Mon, 23 Jul 2007 09:23:26 +0200
- 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 Universität 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 Universität 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 Universität 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 UTC