cassio steel wrote:
> Hello everyone.
> I wonder whether I can run a sparql query which involves freebase,
> from dbpedia sparql endpoint, using linked data.
> For instance, may I retrieve some information about something from
> dbpedia and other informations about the same thing from freebase, on
> the same query from the dbpedia sparql end-point?
>
Well, there's one question here: "do you want the right answers?"
I suppose that somebody could extract RDF statements out of
freebase, load them into the same graph as dbpedia, and then use the
published dbpedia <-> freebase owl:sameAs statements to map them together.
If you did that, AND IF YOU CHECKED THE VALIDITY OF YOUR ANSWERS
(which is NOT standard practice in semweb research, so far as I can
tell) you'd note that the mappings are horribly wrong. The dbpedia <->
freebase mappings are so bad that they'll substantially change the
semantics of dbpedia, even if you never load anything from Freebase;
for instance, you can easily infer bizzare and incorrect statements
such as
dbpedia:Area_11 owl:sameAs dbpedia:Japan.
it just isn't so, and results in the inference of millions of extra
bogus triples, for instance,
dbpedia:Japan rdfs:Label "Area 11"@en .
I found this out when I was trying to establish a 1-1 relationship
between some set of entities and iso codes for countries and
second-level administrative division (... needed that because 90% of the
"Countries" in the dbpedia ontology are fictional or not going
concerns, i.e. "Austria-Hungary", "The Republic Of Atlantis", etc.)
The ISO codes are in freebase, but the dbpedia <-> freebase mappings
were so bad that I decided to give up on Dbpedia as a "primary
reference", use Freebase and just cherry pick selected information
items out of it.
To be fair, I do have freebase <-> dbpedia mappings that are much
better quality than the ones on the dbpedia site and the time might be
right to publish them. The issue here is that there are two ways you
can construct said mapping:
(i) when fb items are created from wikipedia extraction, the wikipedia
page id is recorded in freebase; these can be looked up against the
"page Id" file from dbpedia.
(ii) freebase contains a set of "keys" that name items in freebase;
some of these keys are in the wikipedia namespace, and those can be
mapped to dbpedia pretty easily.
The published mappings look a lot like (ii); the keys are really
promiscuous and link up things that are at most circumstantially related
-- I'd hate to say that they're useless, because they're not, but the
the mapping is too indiscriminate for owl:sameAs to be appropriate.
When I used methodology (i) I found about half as many mappings.
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