以下是我对我的问题的最终解决方案。它比我预期的要复杂，但它确实有效。

问题是查询不接受这些没有父类的类。对于某些联合案例，这可以涵盖 0 个父类、1 个父类或 2 个父类。

SELECT DISTINCT ?leaf ?parentclasses
WHERE {
GRAPH <>
#a leaf is the lowest level class: A class that does not have a subclass
{{{{{
                    
                   
                    
        #I want anything which is a class
        {?leaf rdf:type owl:Class.}
                    
#squeezed 
        filter strstarts(str(?leaf), "graph")           
        #keep the leafs that are NOT The values whereby the subclass is not empty. 
 (double negative for removing leafs where the subclass has a subclass below it)
            FILTER NOT EXISTS {?subclass rdfs:subClassOf ?leaf 
            FILTER (?subclass != owl:Nothing ) }
 }              
                {
         {?leaf rdfs:subClassOf ?superclass .}
               
 #grab dutch label if available
optional {
?superclass skos:prefLabel ?superclassnllabel .
filter( langMatches(lang(?superclassnllabel),"nl") )
}

# take either as the label, but dutch over empty
                bind( coalesce( ?superclassnllabel, replace(str(? 
superclass),"^[^#]*#", "" ) ) as ?superclasslabel )
            
                {
                    
                {?superclass rdfs:subClassOf ?supersuperclass.}
                

        #grab dutch label if available
 
?supersuperclass skos:prefLabel ?supersuperclassnllabel .
                    filter( langMatches(lang(?supersuperclassnllabel),"nl") )



 # take either as the label, but dutch over empty
                    bind( coalesce( ?supersuperclassnllabel, replace(str(? 
 supersuperclass),"^[^#]*#", "" ) ) as ?supersuperclasslabel )
                BIND(concat(str(?superclasslabel), str(" - "), str(? 
supersuperclasslabel) ) as ?parentclasses)
                }
                union
                {
                    
                    {?superclass ?p ?o.filter(!isblank(?superclass))}
                    FILTER NOT EXISTS {?superclass rdfs:subClassOf ?supersuperclass}
                        BIND(concat(str(?superclasslabel), str(" - "), str("Top 
Concept") ) as ?parentclasses) 
                #concatenate the two parentclass variables into one    
                
                }


        
            }
            }
            
            union
            {
                   #figure this out, WHY IS IT HERE? 
                {?leaf rdf:type owl:Class .filter(!isblank(?leaf))}
                FILTER strstarts(str(?leaf), "graph") 
                FILTER NOT EXISTS {?leaf rdfs:subClassOf ?superclass}
                FILTER NOT EXISTS {?subclass rdfs:subClassOf ?leaf 
                FILTER (?subclass != owl:Nothing ) }
                BIND (str("Top Class")  as ?parentclasses )
                   
                
                }

            }}}}