However, all the relevant TaskFactories are in org.cytoscape.tableimport.internal, and are not available, and what could have been a relevant CyAction is commented out in abcaf57d095a1be7316681628d46973d6f63e626, possibly for very good reasons.
Making ontology loading part of the Cytoscape API needs to happen before this is addressed.
There isn't a means by which to import ontologies via CyREST.
The steps to achieve this via the GUI are outlined here: http://manual.cytoscape.org/en/stable/Ontology_and_Annotation_Import.html
However, all the relevant TaskFactories are in org.cytoscape.tableimport.internal, and are not available, and what could have been a relevant CyAction is commented out in abcaf57d095a1be7316681628d46973d6f63e626, possibly for very good reasons.
Making ontology loading part of the Cytoscape API needs to happen before this is addressed.