prolog vs starting point

prolog

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

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

starting point

noun
  • The first steps when commencing an activity. 

  • The place where a journey starts. 

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