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Re: Newbie LOD Questions :)

From: Bill Roberts <bill@swirrl.com>
Date: Wed, 28 Oct 2009 22:58:03 +0100
Message-Id: <504BA8DC-C662-484C-866E-B75D5D66B5DD@swirrl.com>
To: nathan@webr3.org, public-lod@w3.org
Hi Nathan

As far as I'm concerned, this list seems a fine place to ask your  
questions.  I don't have time to have a go at answering all of them,  
but I'll make a start.

1) That's a good question.  Ultimately it's up to you.  In the  
semantic web, there is no single "correct" URI for a thing.  In many  
cases it will make sense to use an existing commonly used URI, such as  
the dbpedia one in your example.

2) The philosophy of RDF is that it is decentralised, so there is no  
central authority to define what might be an authoritative URI for a  
thing.  Although it means less certainty, ultimately the decentralised  
approach should be better for scalability.

3) sameAs indicates that two URIs refer to the same thing (ie they are  
two different identifers for the same thing - don't mix it up with  
URIs of web pages that have information about that thing) - and this   
allows you to infer that if A owl:sameAs B then any statement about A  
is also true about B.

3a) In web jargon, I think you might be mixing up 'information' and  
'non-information' resources.  What I mean is that you are mixing up a  
URI as an identifier for a thing, and a URI for a document on the web  
which happens to hold a bunch of RDF.  I don't think sameAs is really  
relevant for the mirror example you presented.

I'll have to stop there for now - hopefully you'll get further  
responses to address your other questions.

Hope that helps

Bill Roberts

On 28 Oct 2009, at 19:04, Nathan wrote:

> Hi All,
> Apologies if this is the wrong place to ask questions about linked  
> data; however not sure where else to turn at the minute! and again  
> as it's quite a long list.
> worth noting the following link for most of the following questions:
> http://sameas.org/text?uri=http%3A%2F%2Fdbpedia.org%2Fresource 
> %2FLondon
> 1] Let's say I'm writing an article about London, England; which one  
> of the many URI's do I reference that my data is "about"?
> 2] Would there be scope for a single globally unique identifier /  
> URI to represent "London, England"? one which rather than holding  
> information about London (like http://dbpedia.org/resource/London),  
> essentially held a set of sameas items which everyone could use when  
> publishing data "about" "London, England" (like the data at the  
> sameas.org link above).
> 3] If sameAs indicates that two URI references contain information  
> about the same thing; how do we assert that two URI's contain the  
> same information about the same thing (ie identical data)?
> 3a] as [3], mirrors are common on the net, us1.domain us2.domain  
> etc; each one containing the same information; as above how would  
> one indicate that the data is the same? considering that ...
> - the data is identical, no way to inject in a "sameas" in to the rdf
> - one 3rd party may reference the uri http://us1.domain.com/something.rdf 
>  whilst another 3rd party references http://us2.domain.com/something.rdf
> both are the same data, but no correlation between the two exists  
> anywhere to say they are the same thing.
> - it stands to reason that the ideal is a single endpoint and  
> mirrors behind the scenes without any http 30* redirects ever being  
> returned to the client, however this won't always be the case so  
> what syntax can we use in this scenario?
> [4] Are there any conventions or guidelines for combining data and  
> resolving discrepancies? for instance to get all data about london  
> one would theoretically have to combine all the data from the uri's  
> referenced at (the sameas.org link aforementioned), but surely if  
> you combined all data together then you'd get both duplicates and  
> differences in the data.. which is fact etc.
> [4a] Likewise with people - I have multiple social profiles all  
> about "me" but surely in the near future multiple URI's will each  
> represent #me; I think we can safely say that not all of these will  
> be linked with sameas, and further still which one should X person  
> use when referencing information about "me"?
> [4b] Is there any method to mark which is the preferred source of  
> information (and verify it)? at the minute it seems like it would be  
> very simple to publish a vast amount of inaccurate data in triples  
> and it appears the current mentality would be to take it for granted  
> that the information IS fact.
> DC vs ctag and FOAF
> For RDFa we have ctag and maker; which to me seems very exact:
> <span rel="ctag:means" resource="http://dbpedia.org/page/Washington"/>
> <span rel="foaf:maker" resource="http://faviki.com/person/ 
> example#me"/>
> but in dublin core we have the very loose
> <span property="dc:subject">Washington</span>
> <span property="dc:creator">Example</span>
> I'm aware one can couple both dc and ctag/foaf in RDFa; but should  
> we be replacing dc values wherever possible with the more precise  
> ctag/foaf? (and indeed in our standard rdf data?)
> A quick question about the usage of RDFa; previously I had always  
> envisioned RDFa documents to contain a lot of inline rdf markup; I'm  
> aware of the problems in picking up a term in the middle of a block  
> of text and wrapping it in the appropriate notation; however my  
> question is am I wrong in thinking this is the main use/advantage?  
> in most cases where I've sen XHTML+RDFa (like uriburner etc) it's  
> been more case of using RDFa to display human readable RDF; as  
> opposed to human targeted article with rfda embedded in-place / in- 
> line. Does anybody have any examples of a full RDFa demo site; not  
> just with the normal dc/foaf and tags but fully enriched with  
> detected semantic terms highlighted, linked and wrapped in rdfa,  
> inline..?
> And finally any info on creating a set/document which comprises of  
> or includes / references items in other datasets? (I may really show  
> my newbie-ness here) - what I mean is say I'm making an RDFa page  
> about London, and in that I mention the population; I don't want to  
> have the population in document or in the rdf, I do however want to  
> link through to the triple which holds the population for london in  
> dbpedia or a geo set and have that in my rdfa. So where I could have:
> (spo)
> london-population-7556900
> I'd rather have:
> london-population-{some link to dbpedia-owl:populationTotal value in  
> dbpedia's rdf for london)
> Thus I'm saying that london's population is {found here} and it'd be  
> nice if it can also be pulled in and displayed through in an XHTML 
> +RDFa document by possibly content="URI#dbpedia-owl:populationTotal"  
> or suchlike.
> Not sure if I explained that properly, perhaps just simply how do I  
> reference a single triple rather than a full rdf set; or am I way of  
> target?
> Many Thanks in advance for any answers, comments etc & apologies  
> again if it's the wrong place to ask!
> Nathan
Received on Wednesday, 28 October 2009 21:58:38 UTC

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