title: Hibernate Basic value types 'yes_no' and 'true_false'
body: <p>In Hibernate a lot of Basic value types. 
  One of them is '<code>yes_no</code>' and '<code>true_false</code>'. And I was wondering what the fundamental difference between these two types?
  I see that in the database for the type of '<code>yes_no</code>' written '<code>Y or N'</code> and from <code>'true_false'</code> written <code>'F or T'</code> and no more difference. Then why do we need these two types? 
  Why can not we do just one?</p>