Re: Matching literals of unknown langs

[Andy Seaborne]

On 17/12/12 22:04, Olivier Rossel wrote:
Thqt sounds like q
On Mon, Dec 17, 2012 at 10:03 PM, Andy Seaborne <a...@apache.org> wrote:
On 17/12/12 11:41, Olivier Rossel wrote:

Hello.

The SPARQL spec says:
"Florence" is not the same RDF literal as "Florence"@fr


and it's just repeating RDF.

...


Now I have to federate-query an italian dataset and the french dbPedia.

As seen above, my french dbPedia contains this literal: "Florence"@fr
My italian dataset contains this literal: "Florence" (with no lang tag).

Here is the federated query:
SELECT DISTINCT ?LocalityITA ?LocalityFR WHERE {
   SERVICE <http://91.121.14.47:6665/sparql/> {
      ?Address <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://www.w3.org/2006/vcard/ns#Address> .
      ?Address <http://www.w3.org/2006/vcard/ns#locality> ?LocalityITA .
      ?LocalityITA <http://www.w3.org/2000/01/rdf-schema#label> ?LabelITA .
   }
   BIND (strbefore(?LabelITA, "(") AS ?Label)
   SERVICE <http://fr.dbpedia.org/sparql>{
      ?LocalityFR <http://www.w3.org/2000/01/rdf-schema#label> ?Label
   }
}


Reformatted:


SELECT DISTINCT  ?LocalityITA ?LocalityFR
WHERE
   { SERVICE <http://91.121.14.47:6665/sparql/>
       { ?Address rdf:type vc:Address .
         ?Address vc:locality ?LocalityITA .
         ?LocalityITA rdfs:label ?LabelITA
       }
     BIND(strbefore(?LabelITA, "(") AS ?Label)
     SERVICE <http://fr.dbpedia.org/sparql>
       { ?LocalityFR rdfs:label ?Label }
   }


You can use str() to get just the lexical form:



How can I tune the query so the literal matching works across lang tags?
Thanks for your help.


You could canonicalise to the simple literal in each SERVICE

SERVICE <....> {
    ....
    ?Address vc:locality ?l .
     BIND(str(?l) AS ?locality)
}



Except fr.dbpedia.org/Virtuoso does not support BIND.

You can get the same effect with a subquery:

SERVICE <....> {
    SELECT (str(?l as ?locality)
    { ...
       ?Address vc:locality ?l .
    }
}

Now you have ?locality without a language tag and can use it as the
canonical term (if yoru app thinks that's safe enough).

         Andy


Ok for the first SERVICE<..> block : str(...) binds a "raw string"
into ?locality.
Now the seconde SERVICE<...> block:
Is a strlang(..., "fr") required to match ?locality against the @fr strings ???
Like this:

SERVICE <myItalianData> {
     SELECT (str(?l) as ?locality)
     {
        ?Address vc:locality ?l .
     }
  }
SERVICE <fr.dbpedia.org> {
     SELECT (?LocalityFR)
     {
        ?LocalityFR rdfs:label strlang(?locality,"fr") .
     }
  }

Or is the ?locality variable bound in a way that says "i am a raw
string, compare me without taking lang-tag into account"?

As usual, thanks for your help, Andy.


?locality is not passed from the first SERVICE to the second - 
evaluation is bottom up and (logically) each SERVICE is evaluted and 
then the results combined in the client.

So I suggest making the SERVICE calls extract the lexical form and then
equate them (via a join) in the client by using ?locality as the output 
of each SERVICE call.

        Andy