human
344) Compute the sum of all building units typed incorrectly as string.
gpt
```sparql
PREFIX xsd:<http://www.w3.org/2001/XMLSchema#>
PREFIX :   <http://example.org/ontology#>

SELECT (SUM(xsd:integer(?val)) AS ?total)
WHERE {
  ?b a :Building ;
     :hasNumberOfUnits ?val .
  FILTER(datatype(?val) = xsd:string)
}
```