anchor.diff:  The first marks it as a property used for optimistic locking, while the latter advices Hibernate OGM
   to refresh that property after writes since its value is managed by the datastore.
   
  -[NOTE]
  +[WARNING]
   ====
   Not mapping the +_rev+ attribute may cause lost updates,
   as Hibernate OGM needs to re-read the current revision before doing an update in this case.
  
positive.code: 
      private String title;
  
      @Column(name="desc")
      private String description;
  
      //getters, setters ...
  
negative.code:     "$type": "entity",
      "$table": "News",
      "title": "On the merits of NoSQL",
      "description": "This paper discuss why NoSQL will save the world for good"
  }
  ----
  ====
  