multiple BIND operations in a single SPARQL query

[Alison Callahan]

Hello all,

I am using TopBraid Composer version 3.5.0 in Ubuntu 11.04. I am trying to execute the following SPARQL query, but I have found that when all four BIND operations are included, the query returns an empty result set.

SELECT ?x

WHERE {

    ?arg1 ns:has_agent ?agent .

    {

        ?agent rdfs:subClassOf ?agent_type .

    }

    UNION

    {

        ?agent rdf:type ?agent_type .

    } .

BIND (IF((?agent_type = <http://bio2rdf.org/chebi:36080>), 1, 0) AS ?x) . #bind number 1

BIND (IF((?agent_type = <http://bio2rdf.org/so:0000236>), -1, 0) AS ?x) . #bind number 2

BIND (IF((?agent_type = <http://bio2rdf.org/chebi:33697>), 1, 0) AS ?x) . #bind number 3

BIND (IF((:subClassAskQuery(?agent_type, <http://bio2rdf.org/chebi:24431>) = true), 1, 0) AS ?x) . #bind number 4

}

:subClassAskQuery is the following:

ASK WHERE {

    ?arg1 (rdfs:subClassOf)* ?arg2 .

}

Strangely, when only bind operations #1 and #4 or bind operations #1-3 are included, the query returns results. The problem seems to be when I combine bind operations #(2, 3 and 4) or (2 and 4) or (3 and 4) -- the result set is empty.

In other queries, I have used multiple bind operations with no problems.

Has anyone else experienced this? Any help is much appreciated!

Thanks,

Alison 

[Gokhan Soydan]

Alison,

The main reason of why the BINDs in your query return an empty result set is that they are all trying to assign values to the same variable ?x. In a SPARQL query, you can assign a value to a variable only once. So, instead of four BINDs, you might need one BIND with nested IFs or four BINDs that assign values to different variables, and then another BIND that would choose what to assign to ?x depending on those vales.

Here is how a BIND with nested IFs would look like in your case:

BIND (IF((?agent_type = <http://bio2rdf.org/chebi:36080>), 1, IF((?agent_type = <http://bio2rdf.org/so:0000236>), -1, IF((?agent_type = <http://bio2rdf.org/chebi:33697>), 1,  IF((:subClassAskQuery(?agent_type, <http://bio2rdf.org/chebi:24431>) = true), 1, 0)))) AS ?x) .

Gokhan

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[Scott Henninger]

Alison; Gokhan's analysis is correct, that you only want one binding
for ?x. Another way to unserstand the query is that for each match of
the graph pattern, a variable can have only one value. In your case
when #1 and #4 were used, there was a value of ?x that was the same
(1 or 0). When bind operations #1-3 were included, ?x matched on the
value 0. For #2, #3, and #4, ?x was bound to different values, such
as ?x=-1 (#2), ?x=1 (#3), ?x=0 (#4). Same for the others.

The IF pattern Gokhan provided should provide a single binding to ?x,
although it's a bit unclear what the intentions of the query are. I.e.
wouldn't a FILTER statement do what you want?.

BTW, with SPARQL 1.1 property paths, the UNION in the WHERE clause can
be replaced by:
?agent rdfs:subClassOf | rdf:type ?agent_type .

-- Scott