Cases in SPARQL 1.1

Question

In the answer to this question here, using SPARQL 1.1, I wanted to bind a new variable based on the value of an existing one. Specifically, I had calculated an ID for the day of the week such that 0 = Sunday, 1 = Monday, 2 = Tuesday, etc. Based on the binding for ?dayID, I wanted to bind ?dayName.

Essentially, I want to code some traditional "cases" structure into SPARQL. Factoring out the day ID calculation for brevity (here hardcoded as Sunday), I tried:

SELECT ?dayName
WHERE { 
    BIND (0 AS ?dayID)

    FILTER (?dayIDCheck = ?dayID)
}
BINDINGS ?dayIDCheck ?dayName {
    (0 "Sunday"@en)
    (1 "Monday"@en)
    (2 "Tuesday"@en)
    (3 "Wednesday"@en)
    (4 "Thursday"@en)
    (5 "Friday"@en)
    (6 "Saturday"@en)
}

Expecting to get ?dayName bound to "Sunday"@en. However, over at sparql.org, I get no answers.

So, concrete questions:

Can anyone explain why the above method doesn't work?
Anyone got an alternative method to implementing "cases" in SPARQL 1.1?

Accepted Answer

6

BINDINGS defines a data table that is joined with the results of the query. It is not the substitution of the variables by the values.

So:

  SELECT * { ... FILTER(?x = 23) }
  BINDINGS ?x { (1) (2) (3) }

execute the { ... FILTER(?x = 23) }, where ?x is unbound, then joins it to the data table. Being unbound the graph pattern evaluates to the empty table, and joining it to the BINDINGS is still empty.

(NB: This was not my preferred design - I preferred the substitution semantics you expected.)

link

answered 25 Mar '12, 12:41

AndyS ♦
9.7k●2●7
accept rate: 32%

Thanks for the answer. That's a real pity.

(25 Mar '12, 12:48) Signified ♦

1

The WG is still open to comments. SPARQL is in the lucky position that there are several real and complete implementations so feedback from depoyed experience before formally completing the spec is possible.

(25 Mar '12, 12:54) AndyS ♦

Answer 2

Here's what I know. That query wouldn't run at all against Virtuoso so I simplified the query slightly and set up a test case against a Jena in-memory model

@Test
public void testBinding() {
    Query q=QueryFactory.create(
        "SELECT ?dayName WHERE {"+ 
        "   FILTER (?dayIDCheck=0)"+
        "}"+
        "BINDINGS ?dayIDCheck ?dayName {"+
        "   (0 'Sunday'@en)"+
        "   (1 'Monday'@en)"+
        "   (2 'Tuesday'@en)"+
        "   (3 'Wednesday'@en)"+
        "   (4 'Thursday'@en)"+
        "   (5 'Friday'@en)"+
        "   (6 'Saturday'@en)" +
        "}"
    );
    Model m=ModelFactory.createDefaultModel();
    QueryExecution qe=QueryExecutionFactory.create(q,m);
    ResultSet r=qe.execSelect();
    assertEquals(1,r.getResultVars().size());
    assertEquals("dayName",r.getResultVars().get(0));
    assertTrue(r.hasNext());
    QuerySolution qs=r.nextSolution();
    assertEquals("Sunday",qs.get("dayName").asLiteral().getLexicalForm());  
}

This test case fails on the assertTrue() so that means no solutions are coming back.

I do get results if I (1) remove the FILTER or (2) write the following for the FILTER

 FILTER(!bound(?dayIDCheck))

so I guess that FILTER and BINDINGS don't work together in Jena the way you and I would expect them to. Perhaps this is a bug in Jena or perhaps we're not reading the SPARQL 1.1 spec correctly.

Note in a case like this, you can always write the old if-then-else ladder...

 IF(?x=0,"Sunday",IF(?x=1,"Monday",IF(?x=2,"Tuesday"...)))

Answer 3

1

Looks like your runtime sets ?dayIDCheck but doesn't bind it.

The query works just fine in my run-time environment and executes as expected.

link

answered 25 Mar '12, 11:33

neumarcx
19●2
accept rate: 0%

edited 25 Mar '12, 11:44

Signified ♦
20.9k●6●22

You mean a bug in the endpoint?

(25 Mar '12, 11:34) Signified ♦

1

yep looks like you run fuseki

(25 Mar '12, 11:40) neumarcx

Cool! What SPARQL engine is lotico running?

(25 Mar '12, 11:47) Signified ♦

1

we run a couple of different engines but for production we have use ARQ on joseki 3.4.4

For the new stuff we play with fuseki, and virtuoso is pretty cool as well. we will also take look at stardog soon.

(25 Mar '12, 11:52) neumarcx

Cases in SPARQL 1.1

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