Base Metrics
Base Metrics comprise of simple metrics, like the counting of classes, axioms, objects etc. These metrics show the quantity of ontology elements.
The difference between the count metrics and the total count metrics is, that the total count metrics takes account of imports from other ontologies.
For the base metrics we chose:
Contents
Class Axioms
Axiom
Axioms are basic statements of an ontology and also the main component, they state what is true in a domain. It is possible to have axioms for classes, properties, datatype definitions, assertions and annotations.
Logical Axiom
Axioms which affect the logical meaning of an ontology are called Logical Axiom.
Class
Classes in ontologies are concepts, these classes can contain other classes or individuals. In other words, a class is a set of individuals. In OWL exists a thing-class, which is a universal class, so every user defined class is a subclass of the thing-class. The corresponding metric count the classes, including the thing-class, to create a view on the quantity of classes.
More information on the metric page for Class Axioms.
Property
In OWL there are two types of properties:
Object property
Object properties link individuals to individuals.
Data property
Other than the Object properties the Data properties link individuals to data values (literals).
Individual Axioms
Individuals
Individuals are the instances of the classes, so they represent the actual object of the domain. There are two types of individuals: named- and anonymous individuals. Named individuals have an explicit name and can be used in every ontology for the same object, while anonymous individuals are used local, only in one ontology. This metric counts all instances, one class is able to have a set of instances.
More details on page Individual Axioms.
Annotation Axioms
Annotation
An OWL ontology contains a set of annotations. These can be used to associate information with an ontology — for example the ontology creator's name. Each annotation consists of an annotation property and an annotation value, and the latter can be a literal, an IRI, or an anonymous individual.
For more see Annotation Axioms.
DL expressivity
Description logics (DL) is a family of formal knowledge representation languages. DLs are used in artificial intelligence to describe and reason about the relevant concepts of an application domain (known as terminological knowledge). The Web Ontology Language [OWL] and its profile is based on DLs. The DL expressivity gets the human readable name of this metric.
Sources
- https://www.w3.org/TR/owl2-syntax/#Axioms
- http://owlapi.sourceforge.net/javadoc/org/semanticweb/owlapi/model/OWLLogicalAxiom.html
- https://www.w3.org/TR/owl-ref/#Class
- https://www.w3.org/TR/owl2-syntax/#Classes
- https://www.w3.org/TR/owl2-syntax/#Individuals
- https://www.w3.org/TR/owl-ref/#Property
- https://www.w3.org/TR/owl2-syntax/#Annotations
- http://owlapi.sourceforge.net/javadoc/org/semanticweb/owlapi/metrics/DLExpressivity.html
- https://en.wikipedia.org/wiki/Description_logic
