How to query Classes with Object Property in Sparq

问题:

Does any one know how to query Classes with Object Property in Sparql? Assume we have an OWL file which contains follows

Human ----(hasPizza)---> Pizzas

Human and Pizzas are classes (or concepts). In SPARQL, this query returns nothing:

select ?x ?y where {
  ?x hasPizza ?y
}

But if I add two individuals (or entities) under those concepts like

Human:Jim ----(hasPizza)---> Pizzas:cheesePizza

that query will return ?x=Jim and ?y=cheesePizza How can I get ?x=Human and ?y=Pizza using SPARQL?

回答1:

Given data like this (in RDF/XML):

<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:owl="http://www.w3.org/2002/07/owl#"
    xmlns:pizzas="http://example.org/pizzas#"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#">
  <owl:Ontology rdf:about="http://example.org/pizzas"/>
  <owl:Class rdf:about="http://example.org/pizzas#Pizza"/>
  <owl:Class rdf:about="http://example.org/pizzas#Human"/>
  <owl:ObjectProperty rdf:about="http://example.org/pizzas#hasPizza">
    <rdfs:domain rdf:resource="http://example.org/pizzas#Human"/>
    <rdfs:range rdf:resource="http://example.org/pizzas#Pizza"/>
  </owl:ObjectProperty>
  <owl:NamedIndividual rdf:about="http://example.org/pizzas#Jim">
    <rdf:type rdf:resource="http://example.org/pizzas#Human"/>
    <pizzas:hasPizza>
      <owl:NamedIndividual rdf:about="http://example.org/pizzas#CheesePizza">
        <rdf:type rdf:resource="http://example.org/pizzas#Pizza"/>
      </owl:NamedIndividual>
    </pizzas:hasPizza>
  </owl:NamedIndividual>
</rdf:RDF>

or the same, in the more readable Turtle:

@prefix :        <http://example.org/pizzas#> .
@prefix rdfs:    <http://www.w3.org/2000/01/rdf-schema#> .
@prefix pizzas:  <http://example.org/pizzas#> .
@prefix owl:     <http://www.w3.org/2002/07/owl#> .
@prefix xsd:     <http://www.w3.org/2001/XMLSchema#> .
@prefix rdf:     <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

pizzas:Jim
      a       pizzas:Human , owl:NamedIndividual ;
      pizzas:hasPizza pizzas:CheesePizza .

pizzas:hasPizza
      a       owl:ObjectProperty ;
      rdfs:domain pizzas:Human ;
      rdfs:range pizzas:Pizza .

pizzas:Human
      a       owl:Class .

pizzas:Pizza
      a       owl:Class .

<http://example.org/pizzas>
      a       owl:Ontology .

pizzas:CheesePizza
      a       pizzas:Pizza , owl:NamedIndividual .

notice that the assertion Jim hasPizza CheesePizza is one triple in the graph. The domain and range axioms for the hasPizza object property are two triples: hasPizza rdfs:domain Human and hasPizza rdfs:range Pizza. SPARQL queries match query patterns against the triples in the graph. Thus, from a query like:

prefix :        <http://example.org/pizzas#>

select ?x ?y where { 
  ?x :hasPizza ?y
}

you will get results such as

$ arq --data pizzas.ttl --query query.sparql
-----------------------
| x    | y            |
=======================
| :Jim | :CheesePizza |
-----------------------

because there is one triple in the graph whose predicate is :hasPizza, and that triple has a :Jim as the subject, and :CheesePizza as the object. It sounds like you're actually asking for the domain and range of the :hasPizza property, which are also easy to retrieve. Use a query like this:

prefix :        <http://example.org/pizzas#>
prefix rdfs:    <http://www.w3.org/2000/01/rdf-schema#>

select ?domain ?range where { 
  :hasPizza rdfs:domain ?domain ;
            rdfs:range ?range .
}

and you'll get results like this:

$ arq --data pizzas.ttl --query query.sparql
-------------------
| domain | range  |
===================
| :Human | :Pizza |
-------------------