Base Metrics

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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:

Class Axioms


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.


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.


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 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


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.