"The ontology consists of concepts or terms (nodes) that are linked by three types of relationships (edges). That means the ontology appears as a direct acyclic graph. The parent and child terms are connected to each other by is_a and part_of relationships. The former is a relation in which the child term is a more restrictive concept than its parent (thus divination is_a traditional_practice). The latter is used to show the inclusion relationships between concepts, for example that a potion_type is part_of a potion."