convenience store vs discount 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 store

noun
  • A type of department store which sell products at prices lower than those asked by other department stores. 

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