The concepts or properties in an ontology often form a hierarchy. The ontology class provides methods for retrieving these hierarchies that can then be easily traversed.
This listing shows output from a sample program for printing the concept hierarchy:

Area

  City

  Country

  Federal State

Weather Station

Measurement

Date

CityWithID

Retrieving a Hierarchy

There are two methods available for retrieving hierarchies: getConceptHierarchy and getPropertyHierarchy. For both, the object returned is of the type Hierarchy.

Hierarchy hierarchy = ontology.getConceptHierarchy(false);

Traversing a Hierarchy

The traversal can be started at the root nodes proceeding the child nodes, or by jumping to a concrete node corresponding to a particular concept or property; the following code snippet demonstrates the first option (see the sample program for a slightly more sophisticated implementation):

for (Term t : hier.getRootTerms()) {

  Node n = hier.getNodeFor(t);

  printNodeHierarchy(n);

}

   

void printNodeHierarchy(Node n) {

  System.out.println(n.getTerm());

  for (Node cn : n.getChildNodes())

    printNodeHierarchy(cn);

}