Specialist is a type of Expert. Investigator is a type of Expert. Investigator is related to Agent. Agent is a type of Official. 
you are likely to find Rifle in/at/on Cabinet. Rifle is related to Dangerous. Dangerous is related to Bomb. 
Specialist --IsA--> Expert <--IsA-- Investigator <--RelatedTo--> Agent --IsA--> Official 
Cabinet <--AtLocation-- Rifle <--RelatedTo--> Dangerous <--RelatedTo--> Bomb 