The following example queries for direct superclasses using Sesame direct types and SKOS prefLabels.

<ac:SparqlDataSource>
   <ac:sparqlQuery><![CDATA[
     PREFIX skos: <http://www.w3.org/2008/05/skos#>
         PREFIX sesame:<http://www.openrdf.org/schema/sesame#>
         SELECT ?record_id ?parent_id ?label 
         WHERE { 
           ?record_id sesame:directSubClassOf ?parent_id
           . OPTIONAL {
               ?record_id skos:prefLabel ?label
           }
           . FILTER isURI(?record_id)
         }  
    ]]></ac:sparqlQuery>
    <ac:file>xxx.rdf</ac:file> 
</ac:SparqlDataSource>

In the object rule empty record separator should be used:

<ac:objectRules rdf:parseType="Collection">
   <ac:ObjectRule rdf:about="recordRule">
   <ac:recordSeparator></ac:recordSeparator>
   <ac:recordIdentifier>record_id</ac:recordIdentifier>
   <ac:recordInformalIdentifier>label</ac:recordInformalIdentifier>
   <ac:propertyRules>
    ...
   </ac:propertyRules>
</ac:ObjectRule>