Checklist for Troubleshooting Empty SPARQL Query Results in RDFLib

Leia D. · 2022-06-15T19:54:55.629Z

Does anyone have a checklist of things to look at when getting empty results in a SPARQL query? The work is in RDFLib. I'm looking at StackOverflow and some other things and am still coming up short. I know the query should return something because the usage view in Protege clearly shows it. And I'm not in a position to share my code. Thanks for any thoughts you have!

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9 comments

· Sorted by Oldest

Andrew P.
·
this is from my exp. w/SQL Leia D. but it may apply here as well. I start removing condition filters one-by-one to see how it affects the result set.
👍1
Leia D.
·
Thank you, Andrew P.. I've found one of the queries that returns null, but am still trying to figure out why that particular one does.
👍1
Evangelos S.
·
maybe it would be better to add line by line in SPARQL query and see what gives each addition
Phil T.
·
Does this offer any insight? https://www.stardog.com/labs/blog/joins-and-nulls-in-sparql/
Leia D.
·
Evangelos S. Phil T. thank you. This has helped. I’m now trying to figure out precisely how to query my restrictions. I've written it in a way I think I should but still empty set. So troubleshooting continues.
Leia D.
·
OK. So to make sure, is this the syntax for querying restrictions? I feel like I've exhausted my troubleshooting. The other parts of my queries are working. I'm trying to find every individual that meets this restriction. I truly welcome the feedback. Thank you. ?restriction rdf:type owl:Restriction . ?restriction owl:onProperty (name of property in my ontology) . ?restriction owl:someValuesFrom (Name of class in my ontology) .

Phil T.

This partial illustration is derived from The African Wildlife Ontology tutorial ontologies: requirements, design, and content

<owl:Class rdf:about="&AfricanWildlifeOntology1;lion">
    <rdfs:subClassOf rdf:resource="&AfricanWildlifeOntology1;animal"/>
    <rdfs:subClassOf>
        <owl:Restriction>
            <owl:onProperty rdf:resource="&AfricanWildlifeOntology1;eats"/>
            <owl:allValuesFrom rdf:resource="&AfricanWildlifeOntology1;herbivore"/>
        </owl:Restriction>
    </rdfs:subClassOf>
    <rdfs:subClassOf>
        <owl:Restriction>
            <owl:onProperty rdf:resource="&AfricanWildlifeOntology1;eats"/>
            <owl:someValuesFrom rdf:resource="&AfricanWildlifeOntology1;Impala"/>
        </owl:Restriction>
    </rdfs:subClassOf>
    <rdfs:comment>Lions are animals that eat only herbivores.</rdfs:comment>
</owl:Class>

<owl:Class rdf:about="&AfricanWildlifeOntology1;Impala">
    <rdfs:subClassOf rdf:resource="&AfricanWildlifeOntology1;animal"/>
    <rdfs:comment>An african antelope http://en.wikipedia.org/wiki/Impala</rdfs:comment>
</owl:Class>

# Which animal eats which other animal?

prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>
prefix owl: <http://www.w3.org/2002/07/owl#>
prefix : <http://www.meteck.org/teaching/ontologies/AfricanWildlifeOntology1.owl#>

select distinct *
where
{
  ?eats rdfs:subClassOf :animal, [
    a owl:Restriction ;
    owl:onProperty :eats;
    owl:someValuesFrom ?eaten
  ] .
  ?eaten rdfs:subClassOf :animal .
  filter(?eats != owl:Nothing)
}

Leia D.
·
Phil T. thank you!!! This is perfect. I've looked at a couple of examples, but nothing as clear as this.
🙏1
Phil T.
·
You’re welcome Leia D.. All due credit to the paper’s author and tutorial producers for a wonderfully concise and relatable example.

Andrew P.
·
this is from my exp. w/SQL Leia D. but it may apply here as well. I start removing condition filters one-by-one to see how it affects the result set.
👍1
Leia D.
·
Thank you, Andrew P.. I've found one of the queries that returns null, but am still trying to figure out why that particular one does.
👍1
Evangelos S.
·
maybe it would be better to add line by line in SPARQL query and see what gives each addition
Phil T.
·
Does this offer any insight? https://www.stardog.com/labs/blog/joins-and-nulls-in-sparql/
Leia D.
·
Evangelos S. Phil T. thank you. This has helped. I’m now trying to figure out precisely how to query my restrictions. I've written it in a way I think I should but still empty set. So troubleshooting continues.
Leia D.
·
OK. So to make sure, is this the syntax for querying restrictions? I feel like I've exhausted my troubleshooting. The other parts of my queries are working. I'm trying to find every individual that meets this restriction. I truly welcome the feedback. Thank you. ?restriction rdf:type owl:Restriction . ?restriction owl:onProperty (name of property in my ontology) . ?restriction owl:someValuesFrom (Name of class in my ontology) .

Phil T.

This partial illustration is derived from The African Wildlife Ontology tutorial ontologies: requirements, design, and content

<owl:Class rdf:about="&AfricanWildlifeOntology1;lion">
    <rdfs:subClassOf rdf:resource="&AfricanWildlifeOntology1;animal"/>
    <rdfs:subClassOf>
        <owl:Restriction>
            <owl:onProperty rdf:resource="&AfricanWildlifeOntology1;eats"/>
            <owl:allValuesFrom rdf:resource="&AfricanWildlifeOntology1;herbivore"/>
        </owl:Restriction>
    </rdfs:subClassOf>
    <rdfs:subClassOf>
        <owl:Restriction>
            <owl:onProperty rdf:resource="&AfricanWildlifeOntology1;eats"/>
            <owl:someValuesFrom rdf:resource="&AfricanWildlifeOntology1;Impala"/>
        </owl:Restriction>
    </rdfs:subClassOf>
    <rdfs:comment>Lions are animals that eat only herbivores.</rdfs:comment>
</owl:Class>

<owl:Class rdf:about="&AfricanWildlifeOntology1;Impala">
    <rdfs:subClassOf rdf:resource="&AfricanWildlifeOntology1;animal"/>
    <rdfs:comment>An african antelope http://en.wikipedia.org/wiki/Impala</rdfs:comment>
</owl:Class>

# Which animal eats which other animal?

prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>
prefix owl: <http://www.w3.org/2002/07/owl#>
prefix : <http://www.meteck.org/teaching/ontologies/AfricanWildlifeOntology1.owl#>

select distinct *
where
{
  ?eats rdfs:subClassOf :animal, [
    a owl:Restriction ;
    owl:onProperty :eats;
    owl:someValuesFrom ?eaten
  ] .
  ?eaten rdfs:subClassOf :animal .
  filter(?eats != owl:Nothing)
}

Leia D.
·
Phil T. thank you!!! This is perfect. I've looked at a couple of examples, but nothing as clear as this.
🙏1
Phil T.
·
You’re welcome Leia D.. All due credit to the paper’s author and tutorial producers for a wonderfully concise and relatable example.