anchor.diff:        attributes="occi.storage.size occi.storage.state";
         actions="http://schemas.ogf.org/occi/infrastructure/storage/action#resize ...";
   */
  -//TODO implement action attribute
  -multiple_category_header
  -  : CATEGORY_HEADER category_header_val (COMMA category_header_val)+
  +multiple_category_header returns [String category]
  +  : CATEGORY_HEADER multi_cat1 = category_header_val
  +    {$category = "["+$multi_cat1.category;}
  +    (
  +      COMMA multi_cat2 = category_header_val
  +      {$category += ", "+$multi_cat2.category;}
  +    )+
  +    {$category += "]";}
   ;
   category_header returns [String category]
     : CATEGORY_HEADER category_header_val
       {$category = "{\"category\":{" + $category_header_val.category + "}}"; }
   ;
   category_header_val returns [String category]
  -  : term_attr scheme_attr class_attr (title_attr | rel_attr | location_attr | cat_attributes_attr)*
  +  : term_attr scheme_attr class_attr (title_attr | rel_attr | location_attr | cat_attributes_attr | action_attr)*
       {
         $category =
         "\"term\":\"" + $term_attr.term + "\", " +
  
positive.code: 
  occi_header:
    (
      multiple_category_header
    | category_header
  
    | multiple_link_header
    | link_header
  
  
negative.code:   REL_ATTR = 'rel';
    LOCATION_ATTR = 'location';
    ATTRIBUTES_ATTR = 'attributes';
    ACTION_ATTR = 'actions';
  
    //Link attribute names
    SELF_ATTR = 'self';
  