What is OWL?

OWL stands for Web Ontology Language and is the W3C standard for writing semantic web ontologies. Currently in its second iteration, it is also referred to as OWL 2.  

OWL axioms can encode information about classes, properties and individuals. This includes subclass hierarchy, property domains and ranges as well as asserting the existence of some types of facts.

There are many different syntaxes in which OWL axioms can be written, but we will focus on functional style syntax (FSS) and Turtle. Here is an example:

“Every dog is a mammal”


SubClassOf( :Dog :Mammal )


:Dog rdfs:subClassOf :Mammal .

OWL axioms can be divided into groups based on what type of reasoning they require to be applied to data. These subsets of OWL are referred to as fragments. The most extensive fragment that can be fully materialised is called OWL RL.

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