Semweb4j/filesQueries/step7

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Step 7: SPARQL ASK

As in step 5, we don't explain the basic setup again.

ASK queries

ASK queries are always executed via model.sparqlAsk which returns a boolean.

"ASK xyz" returns True if xyz evaluates to a non-empty set and False if xyz evaluates to an empty set.

Ask if max is subject or object of any statement:

	System.out.println("Query 1:");
	String queryString = "ASK { { "+max.toSPARQL()+" ?p ?o } UNION { ?s ?p "+max.toSPARQL()+" } }";
	boolean result = model.sparqlAsk(queryString);
	if(result) {
		System.out.println(max+" is in the graph");
	}

where UNION is a set union of these graphs in SPARQL syntax.

Ask if any resource is tagged with tagComputers:

	System.out.println("Query 2:");
	queryString = "ASK { ?resource <"+hasTag+"> "+tagComputers.toSPARQL()+" }";
	if(!model.sparqlAsk(queryString)) {
		System.out.println("nothing is tagged with "+tagComputers);
	}

output

Query 1:
http://xam.de/foaf.rdf.xml#i is in the graph
Query 2:
nothing is tagged with Computers