Ontologies consist of three main things: Classes, Individuals (instances) and properties (relationships) between individuals. To create an ontology, one first has to created calsses.
For each class, a set of Assertions (restrictions) are defined. The assertions specify the conditions that individuals have to have in order to belong to the class. A class hierarchy is also specified by creating sub-classes (using the GUI). The Protege editor will add automatically inherited assertions from parent classes.
The flow for creating ontologies should be as follows : Create class hierarchy → Create properties → Create Assertions based on the newly created properties. This article overviews the important notions (mainly universal and existential assertions) that need to be understood for performing each of these steps using the editor Protege.
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