Re: Dumb SPARQL query problem

Pleasure.
Actually, I found this:
http://answers.semanticweb.com/questions/3530/sparql-query-filtering-by-string

I said it is a pig’s breakfast because you never know what the RDF publisher has decided to do, and need to try everything.
So to match strings efficiently you need to do (at least) four queries:
“cat”
“cat”@en
“cat”^^xsd:string
“cat”@en^^xsd:string or “cat”^^xsd:string@en - I can’t remember which is right, but I think it’s only one of them :-)

Of course if you are matching in SPARQL you can use “… ?o . FILTER (str(?o) = “cat”)…”, but that its likely to be much slower.

This means that you may need to do a lot of queries.
I built something to look for matching strings (of course! - finding sameAs candidates) where the RDF had been gathered from different sources.
Something like
SELECT ?a ?b WHERE { ?a ?p1 ?s . ?b ?p2 ?s }
would have been nice.
I’ll leave it as an exercise to the reader to work out how many queries it takes to genuinely achieve the desired effect without using FILTER and str.

Unfortunately it seems that recent developments have not been much help here, but I may be wrong:
http://www.w3.org/TR/sparql11-query/#matchingRDFLiterals

I guess that the truth is that other people don’t actually build systems that follow your nose to arbitrary Linked Data resources, so they don’t worry about it?
Or am I missing something obvious, and people actually have a good way around this?

To me the problem all comes because knowledge is being represented outside the triple model.
And also because of the XML legacy of RDF, even though everyone keeps saying that is only a serialisation of an abstract model.
Ah well, back in my box.

Cheers.

On 23 Nov 2013, at 11:00, Richard Light <richard@light.demon.co.uk> wrote:

> 
> On 23/11/2013 10:30, Hugh Glaser wrote:
>> Its’ the other bit of the pig’s breakfast.
>> Try an @en
>> 
> Magic!  Thanks.
> 
> Richard
>> On 23 Nov 2013, at 10:18, Richard Light <richard@light.demon.co.uk>
>>  wrote:
>> 
>> 
>>> Hi,
>>> 
>>> Sorry to bother the list, but I'm stumped by what should be a simple SPARQL query.  When applied to the dbpedia end-point [1], this search:
>>> 
>>> PREFIX foaf: 
>>> <http://xmlns.com/foaf/0.1/>
>>> 
>>> PREFIX dbpedia-owl: 
>>> <http://dbpedia.org/ontology/>
>>> 
>>> SELECT *
>>> WHERE {
>>>     ?pers a foaf:Person .
>>>     ?pers foaf:surname "Malik" .
>>>     OPTIONAL {?pers dbpedia-owl:birthDate ?dob }
>>>     OPTIONAL {?pers dbpedia-owl:deathDate ?dod }
>>>     OPTIONAL {?pers dbpedia-owl:placeOfBirth ?pob } 
>>>     OPTIONAL {?pers dbpedia-owl:placeOfDeath ?pod } 
>>> }
>>> LIMIT 100
>>> 
>>> yields no results. Yet if you drop the '?pers foaf:surname "Malik" .' clause, you get a result set which includes a Malik with the desired surname property.  I'm clearly being dumb, but in what way? :-) 
>>> 
>>> (I've tried adding ^^xsd:string to the literal, but no joy.)
>>> 
>>> Thanks,
>>> 
>>> Richard
>>> [1] 
>>> http://dbpedia.org/sparql
>>> 
>>> -- 
>>> Richard Light
>>> 
> 
> -- 
> Richard Light

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Hugh Glaser
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Received on Saturday, 23 November 2013 15:18:03 UTC