variable renaming affects query result

dotNetRDF_variable_issue.fsx

#r "nuget: dotNetRdf.Core"

open VDS.RDF
open VDS.RDF.Parsing

let graph = new Graph()

StringParser.Parse(graph, "
@prefix : <http://example.org/> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .

:age rdfs:domain :Person .
")

// correctly find the solution
graph.ExecuteQuery("
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> 

SELECT *
WHERE {
    ?property rdfs:domain ?class .
    ?sub rdfs:subClassOf* ?class .
}")

// renaming variable ?sub to ?c with get no solution
graph.ExecuteQuery("
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> 

SELECT *
WHERE {
    ?property rdfs:domain ?class .
    ?c rdfs:subClassOf* ?class .
}")

// the following script demonstrates that the issue is present
// for the letters from a to p (and for all uppercase letters)
open VDS.RDF.Query
let query = SparqlParameterizedString "
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> 

SELECT *
WHERE {
    ?property rdfs:domain ?class .
    @sub rdfs:subClassOf* ?class .
}
"
let hasEmptyResult variableName =
  query.SetParameter("sub", graph.CreateVariableNode(variableName))
  printfn "%O" query
  graph.ExecuteQuery(query) :?> SparqlResultSet |> Seq.isEmpty

[ 'a' .. 'z' ]
|> List.map string
|> List.filter hasEmptyResult

[ 'A' .. 'Z' ]
|> List.map string
|> List.filter hasEmptyResult

// experimenting with different values I think
// I found the problem is for variable names
// 'less than' "property"
[
  "az" // no solution
  "aaaaaaaaaaaaaa" // no solution
  "pr" // no solution
  "pro" // no solution
  "propert" // no solution
  "propertx" // no solution
  "property" // found solution
  "ps" // found solution
  "pu" // found solution
  "qz" // found solution
  "zz" // found solution
] |> List.filter hasEmptyResult