Senator is a type of Legislator. Whip is a type of Legislator. Whip is a type of Flexibility. 
Barrier is related to Wall. Wall is part of Cave. Floor is part of Cave. 
Senator --IsA--> Legislator <--IsA-- Whip --IsA--> Flexibility 
Barrier <--RelatedTo--> Wall --PartOf--> Cave <--PartOf-- Floor 