Basic Usage

The main usage for owlapy is to use it for class expression construction. Class expression learning algorithms require such basic structure to work upon. Let’s walk through an example of constructing some class expressions.

In this example we will be using the family ontology, a simple ontology with namespace: http://example.com/family#. Here is a hierarchical diagram that shows the classes and their relationship:

         Thing
           |
        person
       /   |   
   male  female

It contains only one object property which is hasChild and in total there are six persons (individuals), of which four are males and two are females.

Atomic Classes

To represent the classes male, female, and person we can simply use the class OWLClass:

from owlapy.class_expression import OWLClass
from owlapy.iri import IRI

namespace = "http://example.com/family#"

male = OWLClass(IRI(namespace, "male"))
female = OWLClass(IRI(namespace, "female"))
person = OWLClass(IRI(namespace, "person"))

Notice that we created an IRI object for every class. IRI is used to represent an IRI. Every named entity requires an IRI, whereas Anonymous entities does not. However, in owlapy you can create an OWLClass by passing the IRI directly as a string, like so:

male = OWLClass("http://example.com/family#male")

Object Property

To represent the object property hasChild we can use the class OWLObjectProperty:

from owlapy.owl_property import OWLObjectProperty

hasChild = OWLObjectProperty("http://example.com/family#hasChild")

Tip: In owlapy the naming of the classes is made in accordance with the notations from OWL 2 specification but with the word “OWL” in the beginning. Example: “OWLObjectProperty” represents the notation “ObjectProperty”.

Complex class expressions

Now that we have these atomic entities, we can construct more complex class expressions. Let’s say we want to represent all individuals which are male and have at least 1 child.

We already have the concept of male. We need to find the appropriate class for the second part: “have at least 1 child”. In OWL 2 specification that would be ObjectMinCardinality. In owlapy, as we said, we simply add the word “OWL” upfront to find the correct class:

from owlapy.class_expression import OWLObjectMinCardinality

has_at_least_one_child = OWLObjectMinCardinality(
    cardinality = 1, 
    property = hasChild,
    filler = person
)

As you can see, to create an object of class OWLObjectMinCardinality is as easy as that. You specify the cardinality which in this case is 1, the object property where we apply this cardinality restriction and the filler class in case you want to restrict the domain of the class expression. In this case we used person.

Now let’s merge both class expressions together using OWLObjectIntersectionOf:

from owlapy.class_expression import OWLObjectIntersectionOf

ce = OWLObjectIntersectionOf([male, has_at_least_one_child])

Convert to SPARQL, DL or Manchester syntax

Owlapy is not just a library to represent OWL entities, you can also use it to convert owl expressions into other formats:

from owlapy import owl_expression_to_sparql, owl_expression_to_dl, owl_expression_to_manchester

print(owl_expression_to_dl(ce))
# Result: male ⊓ (≥ 1 hasChild.person)

print(owl_expression_to_sparql(ce))
# Result: SELECT DISTINCT ?x WHERE { ?x a <http://example.com/family#male> . { SELECT ?x WHERE { ?x <http://example.com/family#hasChild> ?s_1 . ?s_1 a <http://example.com/family#person> .  } GROUP BY ?x HAVING ( COUNT ( ?s_1 ) >= 1 ) } }

print(owl_expression_to_manchester(ce))
# Result: male and (hasChild min 1 person)

To parse a DL or Manchester expression to owl expression you can use the following convenient methods:

from owlapy import dl_to_owl_expression, manchester_to_owl_expression

print(dl_to_owl_expression("∃ hasChild.male", namespace))
# Result: OWLObjectSomeValuesFrom(property=OWLObjectProperty(IRI('http://example.com/family#','hasChild')),filler=OWLClass(IRI('http://example.com/family#','male')))

print(manchester_to_owl_expression("female and (hasChild max 2 person)", namespace))
# Result: OWLObjectIntersectionOf((OWLClass(IRI('http://example.com/family#','female')), OWLObjectMaxCardinality(property=OWLObjectProperty(IRI('http://example.com/family#','hasChild')),2,filler=OWLClass(IRI('http://example.com/family#','person')))))

In these examples we showed a fraction of owlapy. You can explore the api documentation to learn more about all classes in owlapy and check more examples in the examples directory.