diff --git a/app/models/environment.rb b/app/models/environment.rb
index e3b7f31..7ebb0c7 100644
--- a/app/models/environment.rb
+++ b/app/models/environment.rb
@@ -10,6 +10,7 @@ class Environment < ActiveRecord::Base
   self.partial_updates = false
 
   has_many :tasks, :dependent => :destroy, :as => 'target'
+  has_many :search_terms, :as => :context
 
   IDENTIFY_SCRIPTS = /(php[0-9s]?|[sp]htm[l]?|pl|py|cgi|rb)/
 
diff --git a/app/models/profile.rb b/app/models/profile.rb
index 1506d8d..7054341 100644
--- a/app/models/profile.rb
+++ b/app/models/profile.rb
@@ -138,6 +138,8 @@ class Profile < ActiveRecord::Base
 
   has_many :comments_received, :class_name => 'Comment', :through => :articles, :source => :comments
 
+  has_many :search_terms, :as => :context
+
   def scraps(scrap=nil)
     scrap = scrap.is_a?(Scrap) ? scrap.id : scrap
     scrap.nil? ? Scrap.all_scraps(self) : Scrap.all_scraps(self).find(scrap)
diff --git a/app/models/search_term.rb b/app/models/search_term.rb
new file mode 100644
index 0000000..4d9c9ab
--- /dev/null
+++ b/app/models/search_term.rb
@@ -0,0 +1,34 @@
+class SearchTerm < ActiveRecord::Base
+  validates_presence_of :term, :context
+  validates_uniqueness_of :term, :scope => [:context_id, :context_type, :asset]
+
+  belongs_to :context, :polymorphic => true
+  has_many :occurrences, :class_name => 'SearchTermOccurrence'
+
+  attr_accessible :term, :context, :asset
+
+  def self.calculate_scores
+    find_each { |search_term| search_term.calculate_score }
+  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
+
+  before_save :calculate_score
+
+  def calculate_score
+    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
+    else
+      self.score = 0
+    end
+  end
+end
diff --git a/app/models/search_term_occurrence.rb b/app/models/search_term_occurrence.rb
new file mode 100644
index 0000000..fc3e20a
--- /dev/null
+++ b/app/models/search_term_occurrence.rb
@@ -0,0 +1,10 @@
+class SearchTermOccurrence < ActiveRecord::Base
+  belongs_to :search_term
+  validates_presence_of :search_term
+  attr_accessible :search_term, :created_at, :total, :indexed
+
+  #TODO Verify this value
+  EXPIRATION_TIME = 1.month
+
+  scope :valid, :conditions => ["search_term_occurrences.created_at >= ?", DateTime.now - EXPIRATION_TIME]
+end
diff --git a/db/migrate/20140507195924_create_search_term_occurrences.rb b/db/migrate/20140507195924_create_search_term_occurrences.rb
new file mode 100644
index 0000000..f4f8793
--- /dev/null
+++ b/db/migrate/20140507195924_create_search_term_occurrences.rb
@@ -0,0 +1,16 @@
+class CreateSearchTermOccurrences < ActiveRecord::Migration
+  def up
+    create_table :search_term_occurrences do |t|
+      t.references   :search_term
+      t.datetime     :created_at
+      t.integer      :total, :default => 0
+      t.integer      :indexed, :default => 0
+    end
+    add_index :search_term_occurrences, :created_at
+  end
+
+  def down
+    remove_index :search_term_occurrences, :created_at
+    drop_table :search_term_occurrences
+  end
+end
diff --git a/db/migrate/20140507205338_create_search_terms.rb b/db/migrate/20140507205338_create_search_terms.rb
new file mode 100644
index 0000000..2e01a8d
--- /dev/null
+++ b/db/migrate/20140507205338_create_search_terms.rb
@@ -0,0 +1,17 @@
+class CreateSearchTerms < ActiveRecord::Migration
+  def up
+    create_table :search_terms do |t|
+      t.string      :term
+      t.references  :context, :polymorphic => true
+      t.string      :asset, :default => 'all'
+      t.float       :score, :default => 0
+    end
+
+    add_index :search_terms, [:term, :asset, :score]
+  end
+
+  def down
+    remove_index :search_terms, [:term, :asset, :score]
+    drop_table :search_terms
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 98d6ffb..fa3123d 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20140408172149) do
+ActiveRecord::Schema.define(:version => 20140507205338) do
 
   create_table "abuse_reports", :force => true do |t|
     t.integer  "reporter_id"
@@ -550,6 +550,25 @@ ActiveRecord::Schema.define(:version => 20140408172149) do
     t.integer  "context_id"
   end
 
+  create_table "search_term_occurrences", :force => true do |t|
+    t.integer  "search_term_id"
+    t.datetime "created_at"
+    t.integer  "total",          :default => 0
+    t.integer  "indexed",        :default => 0
+  end
+
+  add_index "search_term_occurrences", ["created_at"], :name => "index_search_term_occurrences_on_created_at"
+
+  create_table "search_terms", :force => true do |t|
+    t.string  "term"
+    t.integer "context_id"
+    t.string  "context_type"
+    t.string  "asset",        :default => "all"
+    t.float   "score",        :default => 0.0
+  end
+
+  add_index "search_terms", ["term", "asset", "score"], :name => "index_search_terms_on_term_and_asset_and_score"
+
   create_table "sessions", :force => true do |t|
     t.string   "session_id", :null => false
     t.text     "data"
diff --git a/test/unit/search_term_occurrence_test.rb b/test/unit/search_term_occurrence_test.rb
new file mode 100644
index 0000000..7bfedae
--- /dev/null
+++ b/test/unit/search_term_occurrence_test.rb
@@ -0,0 +1,30 @@
+require 'test_helper'
+
+class SearchTermOccurrenceTest < ActiveSupport::TestCase
+
+  def setup
+    @search_term = SearchTerm.find_or_create('universe', Environment.default)
+  end
+
+  attr_reader :search_term
+
+  should 'have term' do
+    search_term_occurrence = SearchTermOccurrence.new
+    assert !search_term_occurrence.valid?
+    assert search_term_occurrence.errors.has_key?(:search_term)
+  end
+
+  should 'create a search term occurence' do
+    assert_nothing_raised do
+      SearchTermOccurrence.create!(:search_term => search_term)
+    end
+  end
+
+  should 'fetch only valid occurrences' do
+    o1 = SearchTermOccurrence.create!(:search_term => search_term)
+    o2 = SearchTermOccurrence.create!(:search_term => search_term)
+    o3 = SearchTermOccurrence.create!(:search_term => search_term, :created_at => DateTime.now - (SearchTermOccurrence::EXPIRATION_TIME + 1.day))
+
+    assert_equivalent [o1,o2], search_term.occurrences.valid
+  end
+end
diff --git a/test/unit/search_term_test.rb b/test/unit/search_term_test.rb
new file mode 100644
index 0000000..6b6fd4a
--- /dev/null
+++ b/test/unit/search_term_test.rb
@@ -0,0 +1,81 @@
+require 'test_helper'
+
+class SearchTermTest < ActiveSupport::TestCase
+  should 'have term' do
+    search_term = SearchTerm.new
+    assert !search_term.valid?
+    assert search_term.errors.has_key?(:term)
+  end
+
+  should 'have context' do
+    search_term = SearchTerm.new
+    assert !search_term.valid?
+    assert search_term.errors.has_key?(:context)
+  end
+
+  should 'have unique term within specific context and asset' do
+    SearchTerm.create!(:term => 'galaxy', :context => Environment.default, :asset => 'universe')
+    search_term = SearchTerm.new(:term => 'galaxy', :context => Environment.default, :asset => 'universe')
+    search_term.valid?
+    assert search_term.errors.has_key?(:term)
+
+    search_term.asset = 'alternate_universe'
+    search_term.valid?
+    assert !search_term.errors.has_key?(:term)
+  end
+
+  should 'create a search term' do
+    assert_nothing_raised do
+      SearchTerm.create!(:term => 'universe', :context => Environment.default)
+    end
+  end
+
+  should 'find or create by term' do
+    assert_difference 'SearchTerm.count', 1 do
+      SearchTerm.find_or_create('universe', Environment.default)
+      search_term = SearchTerm.find_or_create('universe', Environment.default)
+      assert_equal 'universe', search_term.term
+    end
+  end
+
+  should 'have occurrences' do
+    search_term = SearchTerm.find_or_create('universe', Environment.default)
+    o1 = SearchTermOccurrence.create!(:search_term => search_term)
+    o2 = SearchTermOccurrence.create!(:search_term => search_term)
+
+    assert_equivalent [o1,o2], search_term.occurrences
+  end
+
+  should 'calculate score' do
+    search_term = SearchTerm.find_or_create('universe', Environment.default)
+    occurrence = SearchTermOccurrence.create!(:search_term => search_term, :total => 10, :indexed => 3)
+    search_term.save!
+    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.save!
+    assert search_term.score == 0, "Considered expired occurrence to calculate the score."
+  end
+
+  should 'calculate search_terms scores' do
+    st1 = SearchTerm.create!(:term => 'st1')
+    SearchTermOccurrence.create!(:search_term => st1, :total => 10, :indexed => 3)
+    SearchTermOccurrence.create!(:search_term => st1, :total => 20, :indexed => 8)
+    SearchTermOccurrence.create!(:search_term => st1, :total => 30, :indexed => 9)
+    st2 = SearchTerm.create!(:term => 'st2')
+    SearchTermOccurrence.create!(:search_term => st2, :total => 10, :indexed => 7)
+    SearchTermOccurrence.create!(:search_term => st2, :total => 20, :indexed => 16)
+    SearchTermOccurrence.create!(:search_term => st2, :total => 30, :indexed => 21)
+
+    SearchTerm.calculate_scores
+    st1.reload
+    st2.reload
+
+    assert st1.score > 0, "Did not calculate st1 score."
+    assert st2.score > 0, "Did not calculate st2 score."
+  end
+
+end
--
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