diff --git a/app/models/search_term.rb b/app/models/search_term.rb
index 8031e89..f45b22a 100644
--- a/app/models/search_term.rb
+++ b/app/models/search_term.rb
@@ -8,26 +8,55 @@ class SearchTerm < ActiveRecord::Base
   attr_accessible :term, :context, :asset
 
   def self.calculate_scores
-    find_each { |search_term| search_term.calculate_score }
+    os = occurrences_scores
+    find_each { |search_term| search_term.calculate_score(os) }
   end
 
   def self.find_or_create(term, context, asset='all')
     context.search_terms.where(:term => term, :asset => asset).first || context.search_terms.create!(:term => term, :asset=> asset)
   end
 
-  def calculate_score
+  # Fast way of getting the occurrences score for each search_term. Ugly but fast!
+  #
+  # Each occurrence of a search_term has a score that is smaller the older the
+  # occurrence happened. We subtract the amount of time between now and the
+  # moment it happened from the total time any occurrence is valid to happen. E.g.:
+  # The expiration time is 100 days and an occurrence happened 3 days ago.
+  # Therefore the score is 97. Them we sum every score to get the total score
+  # for a search term.
+  def self.occurrences_scores
+    ActiveSupport::OrderedHash[*ActiveRecord::Base.connection.execute(
+      joins(:occurrences).
+      select("search_terms.id, sum(#{SearchTermOccurrence::EXPIRATION_TIME.to_i} - extract(epoch from (now() - search_term_occurrences.created_at))) as value").
+      where("search_term_occurrences.created_at > ?", DateTime.now - SearchTermOccurrence::EXPIRATION_TIME).
+      group("search_terms.id").
+      order('value DESC').
+      to_sql
+    ).map {|result| [result['id'].to_i, result['value'].to_i]}.flatten]
+  end
+
+  def calculate_occurrence(occurrences_scores)
+    max_score = occurrences_scores.first[1]
+    (occurrences_scores[id]/max_score.to_f)*100
+  end
+
+  def calculate_relevance(valid_occurrences)
+    indexed = valid_occurrences.last.indexed.to_f
+    total = valid_occurrences.last.total.to_f
+    (1 - indexed/total)*100
+  end
+
+  def calculate_score(occurrences_scores)
     valid_occurrences = occurrences.valid
     if valid_occurrences.present?
-      indexed = valid_occurrences.last.indexed
-      total = valid_occurrences.last.total
-      # Using the formula described on this paper: http://www.soi.city.ac.uk/~ser/papers/RSJ76.pdf
-      current_relevance = indexed > 0 && total >= indexed ? -Math.log(indexed.to_f/total.to_f) : 0
-      # Damp number of occurrences with log function to decrease it's effect over relevance.
-      damped_occurrences = Math.log(valid_occurrences.count)
-      self.score = (damped_occurrences * current_relevance).to_f
+      # These scores vary from 1~100
+      self.occurrence_score = calculate_occurrence(occurrences_scores)
+      self.relevance_score = calculate_relevance(valid_occurrences)
     else
-      self.score = 0
+      self.occurrence_score = 0
+      self.relevance_score = 0
     end
+    self.score = (occurrence_score * relevance_score)/100.0
     self.save!
   end
 end
diff --git a/app/models/search_term_occurrence.rb b/app/models/search_term_occurrence.rb
index fc3e20a..75a8f29 100644
--- a/app/models/search_term_occurrence.rb
+++ b/app/models/search_term_occurrence.rb
@@ -3,8 +3,7 @@ class SearchTermOccurrence < ActiveRecord::Base
   validates_presence_of :search_term
   attr_accessible :search_term, :created_at, :total, :indexed
 
-  #TODO Verify this value
-  EXPIRATION_TIME = 1.month
+  EXPIRATION_TIME = 1.year
 
-  scope :valid, :conditions => ["search_term_occurrences.created_at >= ?", DateTime.now - EXPIRATION_TIME]
+  scope :valid, :conditions => ["search_term_occurrences.created_at > ?", DateTime.now - EXPIRATION_TIME]
 end
diff --git a/db/migrate/20140507205338_create_search_terms.rb b/db/migrate/20140507205338_create_search_terms.rb
index 2e01a8d..6e5fc1f 100644
--- a/db/migrate/20140507205338_create_search_terms.rb
+++ b/db/migrate/20140507205338_create_search_terms.rb
@@ -5,13 +5,23 @@ class CreateSearchTerms < ActiveRecord::Migration
       t.references  :context, :polymorphic => true
       t.string      :asset, :default => 'all'
       t.float       :score, :default => 0
+      t.float       :relevance_score, :default => 0
+      t.float       :occurrence_score, :default => 0
     end
 
-    add_index :search_terms, [:term, :asset, :score]
+    add_index :search_terms, :term
+    add_index :search_terms, :asset
+    add_index :search_terms, :score
+    add_index :search_terms, :relevance_score
+    add_index :search_terms, :occurrence_score
   end
 
   def down
-    remove_index :search_terms, [:term, :asset, :score]
+    remove_index :search_terms, :term
+    remove_index :search_terms, :asset
+    remove_index :search_terms, :score
+    remove_index :search_terms, :relevance_score
+    remove_index :search_terms, :occurrence_score
     drop_table :search_terms
   end
 end
diff --git a/db/schema.rb b/db/schema.rb
index fa3123d..72a9e29 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -563,11 +563,17 @@ ActiveRecord::Schema.define(:version => 20140507205338) do
     t.string  "term"
     t.integer "context_id"
     t.string  "context_type"
-    t.string  "asset",        :default => "all"
-    t.float   "score",        :default => 0.0
+    t.string  "asset",            :default => "all"
+    t.float   "score",            :default => 0.0
+    t.float   "relevance_score",  :default => 0.0
+    t.float   "occurrence_score", :default => 0.0
   end
 
-  add_index "search_terms", ["term", "asset", "score"], :name => "index_search_terms_on_term_and_asset_and_score"
+  add_index "search_terms", ["asset"], :name => "index_search_terms_on_asset"
+  add_index "search_terms", ["occurrence_score"], :name => "index_search_terms_on_occurrence_score"
+  add_index "search_terms", ["relevance_score"], :name => "index_search_terms_on_relevance_score"
+  add_index "search_terms", ["score"], :name => "index_search_terms_on_score"
+  add_index "search_terms", ["term"], :name => "index_search_terms_on_term"
 
   create_table "sessions", :force => true do |t|
     t.string   "session_id", :null => false
diff --git a/test/unit/search_term_test.rb b/test/unit/search_term_test.rb
index faa825d..9cba835 100644
--- a/test/unit/search_term_test.rb
+++ b/test/unit/search_term_test.rb
@@ -51,14 +51,16 @@ class SearchTermTest < ActiveSupport::TestCase
     SearchTermOccurrence.create!(:search_term => search_term, :total => 10, :indexed => 3)
     # Search term must happens at least two times to be considered
     SearchTermOccurrence.create!(:search_term => search_term, :total => 10, :indexed => 3)
-    search_term.calculate_score
+    SearchTerm.calculate_scores
+    search_term.reload
     assert search_term.score > 0, "Score was not calculated."
   end
 
   should 'not consider expired occurrences to calculate the score' do
     search_term = SearchTerm.find_or_create('universe', Environment.default)
     occurrence = SearchTermOccurrence.create!(:search_term => search_term, :total => 10, :indexed => 3, :created_at => DateTime.now - (SearchTermOccurrence::EXPIRATION_TIME + 1.day))
-    search_term.calculate_score
+    SearchTerm.calculate_scores
+    search_term.reload
     assert search_term.score == 0, "Considered expired occurrence to calculate the score."
   end
 
@@ -80,4 +82,19 @@ class SearchTermTest < ActiveSupport::TestCase
     assert st2.score > 0, "Did not calculate st2 score."
   end
 
+  should 'the older the occurrence the less it should influence the score' do
+    st1 = SearchTerm.find_or_create('st1', Environment.default)
+    SearchTermOccurrence.create!(:search_term => st1, :total => 10, :indexed => 3, :created_at => 1.month.ago)
+    SearchTermOccurrence.create!(:search_term => st1, :total => 20, :indexed => 8, :created_at => 1.month.ago)
+    st2 = SearchTerm.find_or_create('st2', Environment.default)
+    SearchTermOccurrence.create!(:search_term => st2, :total => 10, :indexed => 3, :created_at => 2.months.ago)
+    SearchTermOccurrence.create!(:search_term => st2, :total => 20, :indexed => 8, :created_at => 2.months.ago)
+
+    SearchTerm.calculate_scores
+    st1.reload
+    st2.reload
+
+    assert st1.score > st2.score, "Older occurrences are not influencing score less than newer ones."
+  end
+
 end
--
libgit2 0.21.2