Frequency is related to Sound. Song is a type of Sound. Song is related to Singer. Singer is related to Performer. 
Currency is related to Exchange. Sale is a type of Exchange. Sale is related to Commercial. 
Frequency <--RelatedTo--> Sound <--IsA-- Song <--RelatedTo--> Singer <--RelatedTo--> Performer 
Currency <--RelatedTo--> Exchange <--IsA-- Sale <--RelatedTo--> Commercial 