Radiation is related to Lead. Lead is related to Crystal. 
Worker is related to Nurse. Nurse is a different concept from Doctor. Doctor is related to Occupation. Occupation is related to Engineer. 
Radiation <--RelatedTo--> Lead <--RelatedTo--> Crystal 
Worker <--RelatedTo--> Nurse <--DistinctFrom--> Doctor <--RelatedTo--> Occupation <--RelatedTo--> Engineer 