Small script that shows a bug (?) in Comunica. An RDF dataset is parsed and stored in an N3Store and also imported into a local GraphDB (needs to be done manually). A query is executed against both the N3Store and the GraphDB instance. It returns valid results for the N3Store but causes an error when querying GraphDB

test.js

const { QueryEngine } = require("@comunica/query-sparql");
const { Store, Parser } = require("n3");

const rdfData = `
@prefix : </#>.
@prefix ont: <http://example.org/ontology#>.
@prefix m: <http://openmath.org/vocab/math#>.

ont:myApplication_equals
	a m:Application;
	m:arguments
		( [ a m:Variable; m:name "x" ]
		[ a m:Variable; m:name "y" ] );
m:operator "http://www.openmath.org/cd/relation1#eq".`;

const queryString = `
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX OM: <http://openmath.org/vocab/math#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT ?application (count(?argumentList)-1 as ?position) ?operator (COALESCE(?argNam, ?arg) AS ?argName) ?argValue ?argType WHERE {
    ?application OM:arguments/rdf:rest* ?argumentList;
                                      OM:operator ?operator.
    ?argumentList rdf:rest*/rdf:first ?arg.
    ?arg a ?argType.
    # ?argType rdfs:subClassOf OM:Object.
    OPTIONAL {
        ?arg OM:name ?argNam.
    }
    OPTIONAL {
        ?arg OM:value ?argValue.
    }
}
GROUP BY ?application ?argNam ?argValue ?operator ?argType ?arg`;


const n3Store = new Store();
const n3Parser = new Parser();


async function printBindingStream(bindingsStream) {
	// Iterate over the results and print them
	bindingsStream.on('data', (binding) => {
		console.log('----- Binding -----');
		console.log(binding.toString());
	});

	bindingsStream.on('end', () => {
		console.log('Query execution completed');
	});

	bindingsStream.on('error', (error) => {
		console.error('Error executing query:', error);
	});
}

async function runQueryAndPrintBindings(source) {
	try {
		const queryEngine = new QueryEngine();
		const bindingsStream = await queryEngine.queryBindings(queryString, {
			sources: [source],
		});
		printBindingStream(bindingsStream);
	} catch (error) {
		throw new Error(`SPARQL query failed: ${error}`);
	}
}


/**
 * Parses data and stores and stores it in n3Store, then runs query against it
 */
function testQueryingStore() {
	n3Parser.parse(rdfData, (error, quad, prefixes) => {
		if (error) {
			console.error(error);
			return;
		}
		if (quad) {
			n3Store.addQuad(quad);
		} else {
			console.log('Parsing completed');
			runQueryAndPrintBindings(n3Store);
		}
	});
}

/**
 * Runs the query against a local graphDB that contains only the rdfData given above
 */
function testQueryingGraphDB() {
	runQueryAndPrintBindings({type: 'sparql', value: 'http://localhost:7200/repositories/comunica-debug'});
}

testQueryingStore();
testQueryingGraphDB();