Changes in the Prolog format from 2.0 to 2.1:

Additions:

wn_ins.pl: Instance pointers.
 Distinguishes types from instances. E.g. Bill_Clinton is an instance of
 U.S._President rather than a type of U.S._President, but in previous versions
 of WordNet he was listed as a type.
 ins(X,Y) if X is an instance of Y.

   ins(synset_id,synset_id).

 NOTE: Though the order of arguments of ins(X,Y) and hyp(X,Y) may seem
  different (X is an instance of Y, but Y is a hypernym of X), in both
  predicates, the more general synset is the second argument.

wn_sk.pl: Sense keys.
 See senseidx.5WN for the specification. These provide
 ID's that are not dependent on the WordNet data file offsets.
 sk(X,Y,Z) if word Y of synset X has sense key Z.
 ( More info: http://wordnet.princeton.edu/man/senseidx.5WN )

   sk(synset_id,w_num,'sense_key').

wn_syntax.pl: Adjective syntactic markers.
 If noted in the lexicographer files, this indicates a limitation on the
 syntactic position an adjective may have in relation to the noun that it
 modifies. The Prolog DB does not include the parentheses.
 syntax(X,Y,Z) if word Y of synset X has syntax Z.
 ( More info: http://wordnet.princeton.edu/man/wninput.5WN#sect10 )

   syntax(synset_id,w_num,syntax).

Changes:

wn_s.pl:
 Spaces are no longer represented by underscores in words.
   2.0 e.g.: s(100003009,1,'living_thing',n,1,1).
   2.1 e.g.: s(100004359,1,'living thing',n,1,1).

wn_s.pl:
 Adjective markers are no longer appended to the words. They are now
 in a separate operator. (See above: wn_syntax.pl)
   2.0 e.g.: s(300005565,1,'dead(a)',s,6,1).
   2.1 e.g.: s(300005472,1,'dead',s,6,1).
             syntax(300005472,1,a).

wn_g.pl:
 Removed the parentheses surrounding the glosses.
   2.0: g(synset_id,'(gloss)').
   2.1: g(synset_id,'gloss').

wn_cls.pl:
 Now includes w_nums, since some in the database are lexical.
   2.0: cls(synset_id,synset_id,class_type).
   2.1: cls(synset_id,w_num,synset_id,w_num,class_type).

wn_vgp.pl:
 Now includes w_nums, since all in the database are lexical.
   2.0: vgp(synset_id,synset_id).
   2.1: vgp(synset_id,w_num,synset_id,w_num).