title: Google Knowledge Graph Search API @id field
body: <p>I am exploring Google Knowledge Graph Search API, but I can't find relevant documentation explaining the @id field of the response or search entities. 
  For example <code>"@id": "kg:/m/09tm4t4"</code>.</p>
  
  <p>1- What's the lifespan of this id? Is it safe to use it as a key for my own app-specific data that's based on the search results and assume the id is not going to change in the future?</p>
  
  <p>2- All ids I've seen so far have the prefix <code>kg:/m/</code>. I'm thinking of ignoring this prefix in my keys. Would this decision be future-proof? </p>
  
  <p>I haven't seen this format before so any links to documentation of explanation of this format are highly appreciated. </p>