RdfGraph schema retrieval queries for the relation types are not linked by the correct comment variable 
Labels: name: auto:bug, name: area: models

### System Info

langchain = 0.0.251
Python = 3.10.11

### Who can help?

_No response_

### Information

- [ ] The official example notebooks/scripts
- [X] My own modified scripts

### Related Components

- [ ] LLMs/Chat Models
- [ ] Embedding Models
- [ ] Prompts / Prompt Templates / Prompt Selectors
- [ ] Output Parsers
- [ ] Document Loaders
- [ ] Vector Stores / Retrievers
- [ ] Memory
- [ ] Agents / Agent Executors
- [ ] Tools / Toolkits
- [X] Chains
- [ ] Callbacks/Tracing
- [ ] Async

### Reproduction

1. Create an OWL ontology called `dbpedia_sample.ttl` with the following:
``` turtle
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix dcterms: <http://purl.org/dc/terms/> .
@prefix wikidata: <http://www.wikidata.org/entity/> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix prov: <http://www.w3.org/ns/prov#> .
@prefix : <http://dbpedia.org/ontology/> .



:Actor
    a owl:Class ;
    rdfs:comment "An actor or actress is a person who acts in a dramatic production and who works in film, television, theatre, or radio in that capacity."@en ;
    rdfs:label "actor"@en ;
    rdfs:subClassOf :Artist ;
    owl:equivalentClass wikidata:Q33999 ;
    prov:wasDerivedFrom <http://mappings.dbpedia.org/index.php/OntologyClass:Actor> .

:AdministrativeRegion
    a owl:Class ;
    rdfs:comment "A PopulatedPlace under the jurisdiction of an administrative body. This body may administer either a whole region or one or more adjacent Settlements (town administration)"@en ;
    rdfs:label "administrative region"@en ;
    rdfs:subClassOf :Region ;
    owl:equivalentClass <http://schema.org/AdministrativeArea>, wikidata:Q3455524 ;
    prov:wasDerivedFrom <http://mappings.dbpedia.org/index.php/OntologyClass:AdministrativeRegion> .

:birthPlace
    a rdf:Property, owl:ObjectProperty ;
    rdfs:comment "where the person was born"@en ;
    rdfs:domain :Animal ;
    rdfs:label "birth place"@en ;
    rdfs:range :Place ;
    rdfs:subPropertyOf dul:hasLocation ;
    owl:equivalentProperty <http://schema.org/birthPlace>, wikidata:P19 ;
    prov:wasDerivedFrom <http://mappings.dbpedia.org/index.php/OntologyProperty:birthPlace> .
```

2. Run
``` python
from langchain.graphs import RdfGraph

graph = RdfGraph(
    source_file="dbpedia_sample.ttl",
    serialization="ttl",
    standard="owl"
)

print(graph.get_schema)
```

3. Output
```
In the following, each IRI is followed by the local name and optionally its description in parentheses. 
The OWL graph supports the following node types:
<http://dbpedia.org/ontology/Actor> (Actor, An actor or actress is a person who acts in a dramatic production and who works in film, television, theatre, or radio in that capacity.),
<http://dbpedia.org/ontology/AdministrativeRegion> (AdministrativeRegion, A PopulatedPlace under the jurisdiction of an administrative body. This body may administer either a whole region or one or more adjacent Settlements (town administration))
The OWL graph supports the following object properties, i.e., relationships between objects:
<http://dbpedia.org/ontology/birthPlace> (birthPlace, An actor or actress is a person who acts in a dramatic production and who works in film, television, theatre, or radio in that capacity.),
<http://dbpedia.org/ontology/birthPlace> (birthPlace, A PopulatedPlace under the jurisdiction of an administrative body. This body may administer either a whole region or one or more adjacent Settlements (town administration)), <http://dbpedia.org/ontology/birthPlace> (birthPlace, where the person was born)
The OWL graph supports the following data properties, i.e., relationships between objects and literals:
```


### Expected behavior

The issue is that in the SPARQL queries getting the properties the `rdfs:comment` triple pattern always refers to the variable `?cls` which obviously comes from copy/paste code.

For example, getting the RDFS properties via 

``` python
rel_query_rdf = prefixes["rdfs"] + (
    """SELECT DISTINCT ?rel ?com\n"""
    """WHERE { \n"""
    """    ?subj ?rel ?obj . \n"""
    """    OPTIONAL { ?cls rdfs:comment ?com } \n"""
    """}"""
)
```
you can see that the `OPTIONAL` clause refers to `?cls`, but it should be `?rel`.

The same holds for all other queries regarding properties.

The current status leads to a cartesian product of properties and all `rdfs:comment` vlaues in the dataset, which can be horribly large and of course leads to misleading and huge prompts (see the output of my sample in the "reproduction" part)