title: Xtext: Difference between production and datatype rule
body: <p>Can someone explain to me the difference between a production and datatype rule in xtext?
  I know so far that both are parser rules and Datatype Rule returns a primitive EDataype and production rule creates an EObject in the AST.. But I can't see a differnce in their grammar definition:</p>
  
  <p>Dataype Rule:
  Decimal:
   INT '.' INT
  ; </p>
  
  <p>Producion Rule:
  Model:
    (stats += Statement)*
  ;</p>
  
  <p>How did the parser know which is what rule?</p>