Glenn,
On 10/12/2011 08:49 AM, glenn mcdonald wrote:
I agree with this entirely, and it's why I keep insisting that for
most purposes datasets should be expressed using local identifiers,
with all external linkages called out explicitly and/or externally.
owl:sameAs and the use of other people's identifiers for your own
nodes are equally dangerous. If I'm asserting that Brussels is the
capital of Belgium, I'm saying that my notion of Brussels is my notion
of "capital" of my notion of Belgium. I am the authority for that
assertion. Saying that my notion of Brussels, "capital" or Belgium
correspond with anybody else's notion of anything are separate
assertions, for which I do not have the same authority.
I am not sure you are saying the same thing as Hugh.
Who else would be able to make assertions about "your" notion of
Brussels vis-a-vis "some other notion of Brussels" with any more
authority than your own?
Granting your may want to package those separately, which I understood
to be Hugh's point. To favor software that has difficulty with outliers
or contradictory information.
For that matter, the proper interpretation of "correspond" depends on
the purpose: for some things, treating "correspond" as owl:sameAs may
be exactly right, and for some it might be utterly unacceptable. And
it's much easier to map a "corresponds" property to owl:sameAs if you
want to than to rewrite an entire dataset to undo the misapplication
of IDs or owl:sameAs.
Ignoring owl:sameAs statements isn't an option?
Think global, assert local.
Hmmm, so how do diverse data sets get combined? If there is no one who
has the authority to make assertions about subjects outside their own
data sets?
Hope you are having a great day!
Patrick
glenn
On Wed, Oct 12, 2011 at 7:55 AM, Hugh Glaser <[email protected]
<mailto:[email protected]>> wrote:
Hi.
I have argued for a long time that the linkage data (in particular
owl:sameAs and similar links) should not usually be mixed with the
knowledge being published.
Thus, for example as I discussed with Evan for the NYTimes site a
while ago, it is not a good thing to put the owl:sameAs links
(which were produced by a relatively unskilled individual over a
short period of time) at the same status as the other data, which
has been curated over decades by expert reporters.
These sameAs links have potentially very different trust,
provenance, licence, and possibly other non-functional attributes
from the substantive data.
Clearly they have different trust and provenance, but licence may
well be different, as the NYT may want people to take the triples
away to bring traffic to their site, while keeping the other
triples under more restricted licence.
Which brings me to an example of where things have recently gone
badly wrong.
I have reported a bug to the dbpedia team wherein the URIs for
countries have become deeply intertwingled.
Example queries are at the end of this message - they have to
explicitly do the owl:sameAs because the store does not do
owl:sameAs inference, but the outcome is that I can validly infer
answers such as "Maseru is the capital of Belgium".
Of course, mistakes happen, so I am not having a specific go at
dbpedia, which I still think is wonderful.
But the outcome is that I get very bad data from dbpedia.org
<http://dbpedia.org> unexpectedly, which means I (and presumably
anyone else) can't reliably use dbpedia.org <http://dbpedia.org>
at all (because I use an inference engine when I cache the data).
Had the dbpedia.org <http://dbpedia.org> site simply stuck to the
behaviour I was sort of expecting of publishing data from
wikipedia (possibly publishing the linkage data elsewhere) I would
have been in a better position.
One of the issues here is to realise when we are actually adding
knowledge to a triplication process.
It is clear when things like owl:sameAs are added that knowledge
is being added.
However, people probably consider it less clear if URIs from
dbpedia or elsewhere are directly used that they are adding their
own knowledge.
In a similar way, such use introduces knowledge which may have
very different trust and provenance from the data being triplified.
Is this a good way to do things?
I would say not.
I have used a wide variety of Linked Data sources, and have found
problems with almost every one of them (possibly every significant
one).
The problems frequently relate to the extra knowledge that the
triplication process has introduced.
If only I could be given the data without, then I would not have
to reject the dataset.
Thanks for reading this far.
Best
Hugh
Query:
SELECT DISTINCT ?capital WHERE {
?s owl:sameAs <http://dbpedia.org/resource/Belgium> .
?s owl:sameAs ?country .
?country <http://dbpedia.org/ontology/capital> ?capital .
}
As a URI:
http://dbpedia.org/snorql/?query=SELECT+DISTINCT+%3Fcapital+WHERE+%7B%0D%0A+%3Fs+owl%3AsameAs+%3Chttp%3A%2F%2Fdbpedia.org%2Fresource%2FBelgium%3E+.%0D%0A+%3Fs+owl%3AsameAs+%3Fcountry+.%0D%0A+%3Fcountry+%3Chttp%3A%2F%2Fdbpedia.org%2Fontology%2Fcapital%3E+%3Fcapital+.%0D%0A%7D%0D%0A
Output:
capital
http://dbpedia.org/resource/City_of_Brussels
http://dbpedia.org/resource/Maseru
--
Hugh Glaser,
Web and Internet Science
Electronics and Computer Science,
University of Southampton,
Southampton SO17 1BJ
Work: +44 23 8059 3670 <tel:%2B44%2023%208059%203670>, Fax: +44 23
8059 3045 <tel:%2B44%2023%208059%203045>
Mobile: +44 75 9533 4155 <tel:%2B44%2075%209533%204155> , Home:
+44 23 8061 5652 <tel:%2B44%2023%208061%205652>
http://www.ecs.soton.ac.uk/~hg/ <http://www.ecs.soton.ac.uk/%7Ehg/>
--
Patrick Durusau
[email protected]
Chair, V1 - US TAG to JTC 1/SC 34
Convener, JTC 1/SC 34/WG 3 (Topic Maps)
Editor, OpenDocument Format TC (OASIS), Project Editor ISO/IEC 26300
Co-Editor, ISO/IEC 13250-1, 13250-5 (Topic Maps)
Another Word For It (blog): http://tm.durusau.net
Homepage: http://www.durusau.net
Twitter: patrickDurusau
