 PREFIX wfdesc: <http://purl.org/wf4ever/wfdesc#> 
 PREFIX rdfs:    <http://www.w3.org/2000/01/rdf-schema#> 
 PREFIX motifs:  <http://purl.org/wf4ever/motifs.owl#>
 PREFIX wf4ever: <http://purl.org/wf4ever/wf4ever#>
 SELECT ?opA ?outA ?inB ?opB
 WHERE {
        ?opA a wfdesc:Process .
        ?opA wfdesc:hasOutput ?outA .
        ?opB a wfdesc:Process .
        ?opB motifs:hasOperationMotif ?m2 .
        ?m2 a  motifs:UpstreamPolarity .
        ?opB wfdesc:hasInput ?inB .
        ?link a wfdesc:DataLink .
        ?link wfdesc:hasSource ?outA .
        ?link wfdesc:hasSink ?inB .
FILTER (NOT EXISTS { ?opA a wf4ever:StringConstant})
    }