[rdflib-dev] Serious Bug Found with SPARQL Queries

[James Hudson]

I was hoping to get some quick attention on this as this appears to be a 
serious issue with RDFLib. If someone could confirm that I have found a 
bug, that would be helpful.

I submitted the bug report at https://github.com/RDFLib/rdflib/issues/1113


```
import rdflib
from pprint import pprint


data = """
@prefix ex: <http://example.org/> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .


ex:CCCC a rdfs:Class ;
    rdfs:subClassOf ex:AAAA .


ex:DDDD rdfs:subClassOf ex:BBBB,
        ex:AAAA .
"""


g = rdflib.Graph().parse( data = data, format = 'ttl' )


# print( f"{g.serialize( format = 'ttl' ).decode( 'utf8' )}" )


query = """
        PREFIX sch:  <http://schema.org/>
        PREFIX rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
        PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
        
        SELECT ?class ?subclass
        WHERE {        
                ?class rdfs:subClassOf+ ?subclass .                         
      
        }
        ORDER BY ?class ?subclass
        """


qres = g.query( query )


for row in qres:    
              
    aclass    = str( row['class'] )
    subclass  = str( row['subclass'] )
    print( f"{aclass:30s} {subclass:50s}" )  
```


This outputs:

```
http://example.org/CCCC        http://example.org/AAAA                     
      
http://example.org/CCCC        http://example.org/BBBB                     
      
http://example.org/DDDD        http://example.org/AAAA                     
      
http://example.org/DDDD        http://example.org/BBBB   
```


The output declares there is a subClassOf path from CCCC to BBBB and there 
clearly is not. 

I downloaded a SPARQL playground from http://sparql-playground.sib.swiss 
which is trivial to get up and running on a local machine and tried the 
same data an query. The results were:

```
<http://example.org/CCCC> <http://example.org/AAAA>
<http://example.org/DDDD> <http://example.org/AAAA>
<http://example.org/DDDD> <http://example.org/BBBB>
```


which is *exactly* what one expects.

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