- From: Chris Bizer <chris@bizer.de>
- Date: Thu, 26 Jul 2007 12:46:23 +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>
Hi Alan, note that I changed the subject line as there are lots of different things discussed in this thread. > ----- 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: Thursday, July 26, 2007 7:00 AM >Subject: Re: Terminology Question concerning Web Architecture and >Linked Data > > >On Jul 23, 2007, at 3:23 AM, Chris Bizer wrote: > >> 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. > > This is the necessary evil argument. I accept that this practice is > necessary in cases. It was a smart architectural decisinnot to have > the unique name assumption for the Semantic Web, and for OWL's to > provide the ability to take advantage of that state of affairs. But > that doesn't mean that one shouldn't put some serious thought about > the practical difficulties of dealing with a world where there are > multiple names for things, and therefore use the capability > sparingly. Agreed. I think our different view might result from the different domains we are working in. You are working on biology and life science and as I understood there are some "kind of" commonly accepted naming schemata for this domain. I say "kind of" because I was the "URL +1, LSID -1" thread with 148 replies on your mailing list :-) As I'm working on Dbpedia and the LOD project and we are touching lots of domains without accepted naming schemata there. Also note our argument in the tutorial, that if you have a commonly accepted schema like ISBN or ISIN numbers for your domain, put this numbers into your URIs to ease automated link generation, but still use your own URIs so that people can dereference them to YOUR description of the book or stock. (see http://sites.wiwiss.fu-berlin.de/suhl/bizer/pub/LinkedDataTutorial/#autogenerateLinks) It would be interesting to discuss in which cases this is a good practice and in which you should use URIs that have been minted by somebody else. >> 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. > > I would prefer an explicit mechanism for tracking provenance, such > as a vocabulary and protocol for doing so, Jeremy Carol, Pat Hayes, Patrick Stickler and I developed such a vocabulary a while ago. See "Semantic Web Publishing Vocabulary" in the Named Graphs paper http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B758F-4H9YC8X-1&_user=1676895&_coverDate=12%2F31%2F2005&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000054205&_version=1&_urlVersion=0&_userid=1676895&md5=27eb8ebf4f90123d6dc8f8395b7ed4f0#sec22 Requiring everybody to use such a vocabulary would be nice, but does not scale to the complete Web in my opinion. > rather than one which conflicts with another element of your usage. Where do you see conflicts? I think this approach works nicely together with using the Named Graphs data model on the client to represent information that has been retrieved from the Web by dereferencing URIs. See "Semanitc Web Client Library" and the DISCO browser for applications that do exactly this. > owl:sameAs means indistinguishable - the exact same thing. Better > to have objects which are explicitly "commentaries about the thing" > (rather than aliases of the thing), stated by someone at some time > by some authority etc, and than overload the naming mechanism, IMO. I don't say anything on this topic anymore as it has been discussed enough on this list. My take-away from the discussions: For practical reasons it is OK to do this. >> 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. > > When you know. Sure, when you know. Thats why we recommend in our tutorial to properly interlink your data with other data. If enough people do this, then you know. > When you don't, you miss an opportunity to "join", i.e. gather all > the information about an entity you might be interested in. What is the alternative: A central registry for all Web documents talking about the same URI. Very scalable ;-) >> 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. > > There is no basis for this assertion. sameAs isn't a statement about > information quality. It is a statement about identity. No, an owl:sameAs statement connection information from two different data sources, for instance http://dbpedia.org/resource/Harry_Potter_and_the_Half-Blood_Prince owl:sameAs http://www4.wiwiss.fu-berlin.de/bookmashup/books/0747581088, is an external RDF link (in the same way that all other statements that connect different data sources are RDF links). As information providers usually do not set RDF links to information that sucks, setting an RDF Links implies some quality judgement. This is exactly the same as with hypertext links on the classic document web. You can use these links as quality indicator. This is how Google made its first billion. > You could argue, within a community, that it serve this purpose, > and then, with adequate advertising agree among you to do things > this way, but I think that asserting that this is the case in a > tutorial for naive users is somewhat misleading. Certainly this > will not be understood by the SW community at large. I don't think so, the Semantic Web communy knows a lot about WEB technology and they will understand. One just have to look at examples from the classic document Web: Google and alike. >> 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). > > Just so you know where I stand, I find this whole "authority" > business confusing and ripe for misunderstanding, AWWW or not. It is > clear to me that authority doesn't define meaning or correctness. The Web is by definition a distributed open system and that why you will not be able to avoid the "whole authority business" ;-) > Absent that, we need to be careful about saying exactly what this > authority confers. In your tutorial section 5 I honestly don't > understand what differs about the status of the statements in the > authoritative versus non-authoritative versions. Just translate authority with URI owner. In AWWW, the URI owner has a special position as he is the only entity that can officially define what a URI refers to. Therefore, clients can treat information from an URI authority as more trustworthy if they like. The interesting thing about Web architecture is that they can do this, but that the can also do other things for instance, prefer information from a third in their view highly thrustwothy information provider over the information from the URI authority. This point is often forgotten in our discussions, but a fact of life. >> 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. > > Again, this is the necessary evil stance, which I think is > warranted, as you do. Cool. >> 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. > > Yes, but also one that works in the future. Having hidden (as in not > rdf) information about nonstandard interpretations of vocabulary > isn't a robust strategy. I don't see any nonstandard interpretation of any piece of vocabulary here. Maybe you can argue that the TAG work on this is in draft status right now, but I'm pretty sure that it will turn into official findings in the near future without major modifications. These guys have been thinking about this for years now and the dimensions information resource vs. non-information resouce and generic resource vs specific resource are their solution. Which I don't want to question because I don't want to repeat all these discussions. >>> 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? > > I suggested that, for instance, why not have e.g. dbpedia only have > statements associated with *information resources* which are > understood as "community statements about" some subject. It is like > your non-authoritative description, As I said before, this is not practicable right now as there are lots of non-information resources in this world without URIs. > augmenting the metadata with a more explicit description of the > intention, provenance, quality, mechanism by which the statements > were gathered and other information that an agent could use to > decide how to interpret the statements therein. Good idea. > If you were being extra careful you would have another resource for > the data, and point to it so that one could clearly choose, based > on the metadata, whether or not to dereference or use the > "description". Ok, but this is what we are doing. We have 2 information reources (one dereferinging to a HTML representation, one dereferincing to a RDF representation). The only difference is that we have this additional third non-information resource (URI alias) for the reasons outlined in my previous mail. > In your example 1 I wonder whether the author knew of http:// > zitgist.com/music/artist/d71ba53b-23b0-4870-a429-cce6f345763b before > minting http://dbpedia.org/resource/Alec_Empire. If that were the > case, I would say it would have been better to have not minted > http://dbpedia.org/resource/Alec_Empire, instead reusing the > identifier *the author itself* believed to be the proper name of the > resource I think Alec Empire does not know that the Semantic Web exists and therefore also did not mint a URI to himself. This is kind of a problem in our context. > (that's what you are asserting with the owl:sameAs). To to put it > more harshly, doing otherwise would be an unnecessary evil. > >-- > > I'll note another issue: The Creative Commons licenses are about > copyright, which protects expression, not facts. To the extent that > the rdf is data/statement of fact, it is not clear that these > licenses are relevant, and might even be harmful. Sorry, RDF triples on the Web are clearly not facts but claims by their publisher in the same way that any other Web content also has to be concidered as a claim. If this would not be the case, all trust problems would be solved and we could delete the trust layer from the Semantic Web architecture stack. > I suggest you consult a lawyer about this usage - or perhaps > discuss it with the Science Commons counsel - Thinh Nguyen > (thinh@creativecommons.org) This could be interesting. I did not follow the discussions whether data should be considered an expression and is therefore protected by copyright. But I heard with one ear that there was a ruling in the EC that data is considered an expression in most cases. I thought you guys at Creative Commons would take care of following these discussions and provide the community with the right licenses so that we don't have to consult an lawyer for a lot of money. Isn't it by any chance in the scope of the Science Commons project to define the license terms that we would need for our Linking Open Data project? Cheers Chris > I'm hoping to have some time to take a closer look at the whole > tutorial and get back to you with some more comments. (and don't get > me wrong: I'm a big fan of doing this project - but I want the > effort to be the start of a truly scalable enterprise) > > -Alan > > -- 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 Thursday, 26 July 2007 10:50:12 UTC