1:- module(dbpedia_matcher,
    2          [band/1,
    3           has_shared_band_member/3,
    4           has_shared_genre/3,
    5           similarity_by_genre/3,
    6           jaccard/3,
    7           pair_genre_sum_ic/3]).

   19% now builtin
   20%:- use_module(library(tabling)).
   21:- use_module(library(sparqlprog/emulate_builtins)).   22:- use_module(library(sparqlprog/ontologies/dbpedia)).

 has_shared_band_member(?B1, ?B2, ?SharedMember) is nondet

links bands by members in common. E.g. Ronnie James Dio in both Rainbow and Black Sabbath

true if SharedMember is a member of both B1 and B2 (and B1 and B2 are distinct)

   31has_shared_band_member(B1,B2,A) :-
   32        rdf(A,dbont:associatedBand,B1),
   33        rdf(A,dbont:associatedBand,B2),
   34        B1\=B2.

 has_shared_genre(?B1, ?B2, ?SharedGenre) is nondet

links bands by shared genre common.

true if SharedGenre is a genre of both B1 and B2 (and B1 and B2 are distinct)

   42has_shared_genre(B1,B2,A) :-
   43        rdf(B1,dbont:genre,A),
   44        rdf(B2,dbont:genre,A),
   45        B1\=B2.
   46
   47genre_pair(G1,G2,A) :-
   48        rdf(A,dbont:genre,G1),
   49        rdf(A,dbont:genre,G2),
   50        G1\=G2.

 similarity_by_genre(?BandA, ?BandB, ?SumIC)

calculates the jaccard similarity between two entities based on genres in common

the entities should be of similar types (e.g. two bands, or two books)

| genres(A) /\ genres(B) | / | genres(A) \/ genres(B) |

if no genres are in common, then this should equal 0 if all genres are in common, then this should equal 1

note this does not take into account how meaningful it is for a genre to be shared; e.g. sharing the common genre 'pop' counts as much as a rarer genre like 'psytrance'. see further on for IC-based metrics.

   71similarity_by_genre(A,B,Sim) :-
   72        get_all_genres(A,SA),
   73        get_all_genres(B,SB),
   74        jaccard(SA,SB,Sim).
   75
   76jaccard(SA,SB,Sim) :-
   77        ord_intersection(SA,SB,I),
   78        ord_union(SA,SB,U),
   79        length(I,NI),
   80        length(U,NU),
   81        Sim is NI/NU.
   82
   83get_all_genres(Entity,L) :-
   84        service_query_all(dbpedia,G,rdf(Entity,dbont:genre,G),L).
   85
   86
   87
   88:- table get_num_bands/1.

 get_num_bands(?Count) is det

unifies Count with the total number of bands in the database

note this is tabled (cached) so that repeated calls do not invoke new SPARQL queries

   95get_num_bands(Count) :-
   96        ??(dbpedia,num_bands(Count)).
   97num_bands(Count) :-
   98        aggregate(count(distinct(B)),band(B),Count).

 get_genre_num_bands(?Genre, ?Count) is nondet

get_genre_num_bands(+Genre, ?Count) is det

unifies Count with the total number of bands that are categorized as Genre

%%%:- table get_genre_num_bands/2.

  109get_genre_num_bands(G,Count) :-
  110        ??(dbpedia,genre_num_bands(G,Count)).
  111
  112genre_num_bands(G,Count) :-
  113        aggregate_group(count(distinct(B)),[G],(rdf(B,dbont:genre,G),band(B)),Count).

 pair_genre_sum_ic(?BandA, ?BandB, ?SumIC)

for a pair of bands, SumIC is the sum of the ICs of the genres shared in common.

Example: =pair_genre_ic(dbr:'Metallica', dbr:'Megadeth', IC)=

  123pair_genre_sum_ic(A,B,SumIC) :-
  124        get_all_genres(A,SA),
  125        ??(dbpedia,(band(B),has_shared_genre(A,B,_))),
  126        get_all_genres(B,SB),
  127        ord_intersection(SA,SB,I),
  128        debug(dbpedia,'~w vs ~w :: INTERSECTION(~w + ~w) = ~w',[A,B,SA,SB,I]),
  129        aggregate(sum(IC),G^(member(G,I),genre_ic(G,IC)),SumIC).

 genre_ic(?Genre, ?InformationContent:float) is nondet

gets the IC of a particular genre. The higher the IC, the rarer and more 'surprising' or information-rich it is.

for example, many bands are pop, so this would have a low IC. Progressive sludge metal is relatively rare and would have a high IC

InformationContent = -log2( Pr(Genre) )

  141genre_ic(G,IC) :-
  142        get_genre_num_bands(G,Count),
  143        debug(dbpedia,'|bands| in ~w = ~w',[G,Count]),
  144        get_num_bands(Total),
  145        debug(dbpedia,'Total bands = ~w',[Total]),
  146        seval(-log(Count/Total)/log(2), IC)