Model de Events

_form.html.erb

<%= form_for(@event) do |f| %>

  <div class="field">
    <%= f.label :show_me_as %><br />
    <%= f.radio_button :show_me_as, "available" %>
    <%= f.radio_button :show_me_as, "busy" %>
  </div>

events.rb

class Event < ActiveRecord::Base
  # Associations
  belongs_to :user  
  has_many :reminders, :through => :event_reminders
  
  # Validations
  SHOW_AS_AVAILABLE = 'available'
  SHOW_AS_BUSY = 'busy'
  
  validates_presence_of :title, :begin_at, :end_at  
  validates_length_of :title, :minimum => 3
  validates_inclusion_of :show_as, :in => [SHOW_AS_AVAILABLE, SHOW_AS_BUSY]
  
  # Scopes
  scope :not_deleted, where(:deleted_at => nil)  
end

inicial_schema.rb

class InitialSchema < ActiveRecord::Migration
  def self.up   

    # Events
    create_table :events do |t|
      t.references :user, :null => false
      t.string :title
      t.datetime :begin_at, :null => false
      t.datetime :end_at, :null => false      
      t.string :location
      t.text :description      
      t.string :show_as, :default => 'busy'
      t.string :privacy, :default => 'private'  
      t.datetime :deleted_at   
      t.timestamps
    end
    
    add_index :events, :user_id

Qual é a melhor forma para criar constantes, utilizá-las em campos selecionáveis e traduzi-las com locales (i18n)?