convenience store vs discount department store

convenience store

noun
  • A small retail store, often in a residential area, that carries a limited selection of items such as staples, junk food, and drugstore items, and which is open long hours for the convenience of shoppers. 

discount department store

noun
  • A discount store; a department store with reduced prices. 

How often have the words convenience store and discount department store occurred in a corpus of books? (source: Google Ngram Viewer )