overture vs prolog

overture

noun
  • A musical introduction to a piece of music, or a play. 

  • A motion placed before a legislative body, such as the General Assembly of the Church of Scotland. 

  • An approach or proposal made to initiate communication, establish a relationship etc. 

verb
  • To make overtures; to approach with a proposal. 

prolog

noun
  • A speech or section used as an introduction, especially to a play or novel. 

  • A component of a computer program that prepares the computer to execute a routine. 

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