Support for Type Conversion

[tholzheim]

For sorting a query result I need to convert a string literal to an integer literal.
The STRDT function is currently not supported by QLever.

Error message:

Warning
ParseException, cause: Clause "STRDT(?volume_str,xsd:integer)" at line 17:9 Built-in functions (other than aggregates and REGEX) are currently not supported by QLever.

Example query

PREFIX pq: <http://www.wikidata.org/prop/qualifier/> 
PREFIX p: <http://www.wikidata.org/prop/> 
PREFIX schema: <http://schema.org/> 
PREFIX wd: <http://www.wikidata.org/entity/> 
PREFIX wdt: <http://www.wikidata.org/prop/direct/> 
PREFIX wikibase: <http://wikiba.se/ontology#> 
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> 
PREFIX ps: <http://www.wikidata.org/prop/statement/> 
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> 
SELECT DISTINCT ?item ?itemLabel ?volume_str ?volume_int 
WHERE { 
  ?item wdt:P31 wd:Q1143604; 
     wdt:P179 wd:Q27230297; 
     rdfs:label ?itemLabel. 
  FILTER((LANG(?itemLabel)) = "en")
  OPTIONAL { 
    ?item (p:P179/pq:P478) ?volume_str. 
    BIND(STRDT(?volume_str, xsd:integer) as ?volume_int)
    # alternative: BIND(xsd:integer(?volume_str) as ?volume_int)
  } 
} 
ORDER BY ?volume_int

Wikidata Query Service (WQS): https://w.wiki/69fw
QLever: https://qlever.cs.uni-freiburg.de/wikidata/ha05m6