why rdf:type doesn't work with father classes?

Question

In my protege, I state explicitly that the class Symphony is subclass of class Recommendable , as illustrated here: Classes Hierarchy

I've also added some instances to the class Symphony, when I query the Symphony instances, I get results. However, when I query the Recommendable instances, I get nothing.

This is the query for Symphony class:

SELECT DISTINCT  ?subject   WHERE {
  ?subject rdf:type owbes:Symphony
}

And here is the result: Symphony instances query result

This is the query for Recommendable class.

SELECT DISTINCT  ?subject   WHERE {
  ?subject rdf:type owbes:Recommendable
}

This result is empty, as you see here [Recommendable instances query result][3]

Both from the same prefix. What wrong did I do?

This is what's being generated in the owl file:

<owl:Class rdf:about="bla bla bla/recommendation-systems#Symphony">
    <rdfs:subClassOf rdf:resource="bla bla bla/recommendation-systems#Recommendable"/>
</owl:Class>

As you see, I've correctly made Symphony a subclass of Recommendable

I found the solution: Making this query solves the problem

SELECT   ?subject   WHERE {
  ?subject rdf:type ?type.
  ?type rdfs:subClassOf owbes:Recommendable
}

Yet, I don't know why rdf:type doesn't work

<?xml version="1.0"?>
<rdf:RDF xmlns="http://www.semanticweb.org/welovethesemanticweb#"
     xml:base="http://www.semanticweb.org/welovethesemanticweb"
     xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
     xmlns:owl="http://www.w3.org/2002/07/owl#"
     xmlns:xml="http://www.w3.org/XML/1998/namespace"
     xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
     xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
     xmlns:recommendation-systems="http://www.welovethesemanticweb.com/recommendation-systems#">
    <owl:Ontology rdf:about="http://www.semanticweb.org/welovethesemanticweb"/>



    <!-- 
    ///////////////////////////////////////////////////////////////////////////////////////
    //
    // Annotation properties
    //
    ///////////////////////////////////////////////////////////////////////////////////////
     -->




    <!-- http://www.welovethesemanticweb.com/recommendation-systems#hasSimilarityValue -->

    <owl:AnnotationProperty rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#hasSimilarityValue"/>



    <!-- 
    ///////////////////////////////////////////////////////////////////////////////////////
    //
    // Object Properties
    //
    ///////////////////////////////////////////////////////////////////////////////////////
     -->




    <!-- http://www.welovethesemanticweb.com/recommendation-systems#composedBy -->

    <owl:ObjectProperty rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#composedBy">
        <rdfs:subPropertyOf rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#hasArtist"/>
        <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#AsymmetricProperty"/>
        <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#IrreflexiveProperty"/>
        <rdfs:domain rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Symphony"/>
        <rdfs:range rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Composer"/>
        <rdfs:label rdf:datatype="http://www.w3.org/2001/XMLSchema#string">Composed By</rdfs:label>
    </owl:ObjectProperty>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#fromEra -->

    <owl:ObjectProperty rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#fromEra">
        <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#AsymmetricProperty"/>
        <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#IrreflexiveProperty"/>
        <rdfs:domain rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Artist"/>
        <rdfs:range rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#MusicalEra"/>
        <rdfs:label rdf:datatype="http://www.w3.org/2001/XMLSchema#string">Describes the musical era that music is from</rdfs:label>
        <rdfs:label rdf:datatype="http://www.w3.org/2001/XMLSchema#string">From Era</rdfs:label>
        <recommendation-systems:hasSimilarityValue rdf:datatype="http://www.w3.org/2001/XMLSchema#double">0.1</recommendation-systems:hasSimilarityValue>
    </owl:ObjectProperty>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#hasArtist -->

    <owl:ObjectProperty rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#hasArtist">
        <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#AsymmetricProperty"/>
        <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#IrreflexiveProperty"/>
        <rdfs:domain rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Recommendable"/>
        <rdfs:range rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Artist"/>
        <rdfs:comment>Describes the arties of the music</rdfs:comment>
        <rdfs:label rdf:datatype="http://www.w3.org/2001/XMLSchema#string">Has Artist</rdfs:label>
        <recommendation-systems:hasSimilarityValue rdf:datatype="http://www.w3.org/2001/XMLSchema#double">0.4</recommendation-systems:hasSimilarityValue>
    </owl:ObjectProperty>



    <!-- 
    ///////////////////////////////////////////////////////////////////////////////////////
    //
    // Data properties
    //
    ///////////////////////////////////////////////////////////////////////////////////////
     -->




    <!-- http://www.welovethesemanticweb.com/recommendation-systems#contributeToSimilarities -->

    <owl:DatatypeProperty rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#contributeToSimilarities">
        <rdfs:range rdf:resource="http://www.w3.org/2001/XMLSchema#double"/>
    </owl:DatatypeProperty>



    <!-- 
    ///////////////////////////////////////////////////////////////////////////////////////
    //
    // Classes
    //
    ///////////////////////////////////////////////////////////////////////////////////////
     -->




    <!-- http://www.welovethesemanticweb.com/recommendation-systems#Artist -->

    <owl:Class rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#Artist">
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#MusicalEra"/>
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Recommendable"/>
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Song"/>
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Symphony"/>
    </owl:Class>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#Composer -->

    <owl:Class rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#Composer">
        <rdfs:subClassOf rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Artist"/>
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#MusicalEra"/>
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Recommendable"/>
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Song"/>
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Symphony"/>
    </owl:Class>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#MusicalEra -->

    <owl:Class rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#MusicalEra">
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Recommendable"/>
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Singer"/>
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Song"/>
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Symphony"/>
    </owl:Class>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#Recommendable -->

    <owl:Class rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#Recommendable">
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Singer"/>
    </owl:Class>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#Singer -->

    <owl:Class rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#Singer">
        <rdfs:subClassOf rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Artist"/>
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Song"/>
        <owl:disjointWith rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Symphony"/>
    </owl:Class>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#Song -->

    <owl:Class rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#Song">
        <rdfs:subClassOf rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Recommendable"/>
    </owl:Class>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#Symphony -->

    <owl:Class rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#Symphony">
        <rdfs:subClassOf rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Recommendable"/>
    </owl:Class>



    <!-- 
    ///////////////////////////////////////////////////////////////////////////////////////
    //
    // Individuals
    //
    ///////////////////////////////////////////////////////////////////////////////////////
     -->




    <!-- http://www.welovethesemanticweb.com/recommendation-systems#Adele -->

    <owl:NamedIndividual rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#Adele">
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Artist"/>
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Singer"/>
        <recommendation-systems:fromEra rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#current"/>
    </owl:NamedIndividual>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#Beethoven -->

    <owl:NamedIndividual rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#Beethoven">
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Artist"/>
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Composer"/>
        <recommendation-systems:fromEra rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#classical"/>
    </owl:NamedIndividual>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#Dies_Irae -->

    <owl:NamedIndividual rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#Dies_Irae">
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Recommendable"/>
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Symphony"/>
        <recommendation-systems:composedBy rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Mozart"/>
        <recommendation-systems:hasArtist rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Mozart"/>
        <rdfs:label rdf:datatype="http://www.w3.org/2001/XMLSchema#string">Dies Irae</rdfs:label>
    </owl:NamedIndividual>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#Le_nozze_di_Figaro -->

    <owl:NamedIndividual rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#Le_nozze_di_Figaro">
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Recommendable"/>
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Symphony"/>
        <recommendation-systems:composedBy rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Mozart"/>
        <recommendation-systems:hasArtist rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Mozart"/>
        <rdfs:label rdf:datatype="http://www.w3.org/2001/XMLSchema#string">Le Nozze Di Digaro</rdfs:label>
    </owl:NamedIndividual>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#Mozart -->

    <owl:NamedIndividual rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#Mozart">
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Artist"/>
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Composer"/>
        <recommendation-systems:fromEra rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#classical"/>
    </owl:NamedIndividual>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#baroque -->

    <owl:NamedIndividual rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#baroque">
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#MusicalEra"/>
    </owl:NamedIndividual>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#classical -->

    <owl:NamedIndividual rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#classical">
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#MusicalEra"/>
    </owl:NamedIndividual>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#current -->

    <owl:NamedIndividual rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#current">
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#MusicalEra"/>
    </owl:NamedIndividual>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#romantic -->

    <owl:NamedIndividual rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#romantic">
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#MusicalEra"/>
    </owl:NamedIndividual>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#5th_Symphony -->

    <owl:NamedIndividual rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#5th_Symphony">
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Recommendable"/>
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Symphony"/>
        <recommendation-systems:composedBy rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Beethoven"/>
        <recommendation-systems:hasArtist rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Beethoven"/>
        <rdfs:label rdf:datatype="http://www.w3.org/2001/XMLSchema#string">5th Symphony</rdfs:label>
    </owl:NamedIndividual>



    <!-- http://www.welovethesemanticweb.com/recommendation-systems#Requiem:_Sequentia -->

    <owl:NamedIndividual rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#Requiem:_Sequentia">
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Recommendable"/>
        <rdf:type rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Symphony"/>
        <recommendation-systems:composedBy rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Mozart"/>
        <recommendation-systems:hasArtist rdf:resource="http://www.welovethesemanticweb.com/recommendation-systems#Mozart"/>
        <rdfs:label rdf:datatype="http://www.w3.org/2001/XMLSchema#string">Requiem Sequentia</rdfs:label>
    </owl:NamedIndividual>



    <!-- 
    ///////////////////////////////////////////////////////////////////////////////////////
    //
    // General axioms
    //
    ///////////////////////////////////////////////////////////////////////////////////////
     -->

    <rdf:Description>
        <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#AllDifferent"/>
        <owl:distinctMembers rdf:parseType="Collection">
            <rdf:Description rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#baroque"/>
            <rdf:Description rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#classical"/>
            <rdf:Description rdf:about="http://www.welovethesemanticweb.com/recommendation-systems#romantic"/>
        </owl:distinctMembers>
    </rdf:Description>
</rdf:RDF>



<!-- Generated by the OWL API (version 4.1.3.20151118-2017) https://github.com/owlcs/owlapi -->

Answer 1

When a class C is declared as a subclass of class D, you can infer that an instance of C is also an instance of D. However, that process of inference is something that you need a reasoner for. If you're not using a reasoner, you won't automatically get that result. In short, you're asking for a triple of the form

?subject rdf:type owbes:Recommendable

but that's not in the data. What's in the data is two triples:

?subject rdf:type owbes:Symphony  
owbes:Symphony rdfs:subClassOf owbes:Recommendable

In this case, you can actually get by using a SPARQL query with property paths; you don't need a full reasoner. You can use a query like this:

select ?subject where {
    ?subject rdf:type/rdfs:subClassOf* owbes:Recommendable
}

This says to find subjects that have a type that's linked to owbes:Recommendable by a chain (possibly of length zero) of rdfs:subClassOf properties. In practice, that means to find ?subjects that are owbes:Recommendable or one of its subclasses.

For some more information, see:

• Using SPARQL for limited RDFS and OWL reasoning
• how to do reasoning in Jena via Sparql Query