LANG support or work-around

[WolfgangFahl]

http://qlever.wikidata.dbis.rwth-aachen.de/wikidata/tVCucU

Not supported: The LANG function is currently only supported in the construct FILTER(LANG(?variable) = "langtag" by QLever

isn't there a workaround? why does e.g. http://qlever.wikidata.dbis.rwth-aachen.de/wikidata/k1889D not work?

[hannahbast]

@WolfgangFahl It is problematic when you post links to an endpoint that is down most of the time. I clicked on your links several times over the last week and always received an 404.

[WolfgangFahl]

@hannahbast - i didn't now that the links are not persistent - where can i file a ticket for or find the documentation to enable such a feature?

[joka921]

@WolfgangFahl The official qlever-ui has a database that keeps the short links alive. But as it seems you are not using this but are using your own UI, so making these links persistent is your responsibility. (The persistent query links are not a feature of the QLever backend, but of the UI which is used in top of it).

As for your actual question: I recently had an idea for an efficient implementation of the general case of the LANG function which might happen as a byproduct of more prominent feature, so this might appear some time in the future.

[Rdataflow]

@joka921 it would be great to see proper LANG() support

I'd like to sponsor some simple test cases here https://qlever.cs.uni-freiburg.de/wikidata/CzM2Kb HTH for your upcoming work :crossed_fingers:

# test cases for `LANG()` implementation
SELECT * WHERE {
  # test case 1 - check returns "" if literal has no language tag 
  VALUES ?something { "aLiteralWithoutLanguageTag" }
  FILTER(LANG(?something) = "")

  # test case 2 - check returns the language tag of literal, if it has one
  VALUES ?anotherthing { "anotherLiteralWithLanguageTagDE"@de }
  FILTER(LANG(?anotherthing) = "de")

  # test case 3 - check returns the language tag of literal, if it has one
  BIND(STRLANG("anotherLiteralWithLanguageTagEN", "en") AS ?anotherthing2)
  FILTER(LANG(?anotherthing2) = "en")
}

# expected output: (according to the w3c recommendation)
# ?something                  ?anotherthing                    ?anotherthing2
# aLiteralWithoutLanguageTag  anotherLiteralWithLanguageTagDE  anotherLiteralWithLanguageTagEN

# actual output: (qlever:latest as of "2024-06-15"^^xsd:date)
# ?something                  ?anotherthing
# [[empty set]]