PayRoll application, embedded in Rails, borrowing from Use Case Driven Architecture and DCI

your_application.rb

## PayRoll Application Gem

# lib/pay_roll/pay_day_service.rb
# Consider this Use Case as the Context in DCI
#
class PayRoll::PayDayService
  def initialize(date=Date.today)
    @date = date

    # Employee could be any data source from the host, 
    # in this example Rails/Active Record
    #
    @employees ||= Employee.active
    @employees.each { |e| e.extend(PayCheckRecipient) }
  end

  def execute
    @employees.each do |e|
      if e.pay_date?(@date)
        pc = PayCheck.new(e.calculate_pay(@date))
        e.send_pay(pc)
      end
    end
  end
end

# lib/pay_roll/pay_check_recipient.rb
# Consider this the Role in DCI
#
module PayRoll::PayCheckRecipient
  def pay_date?(date)
    # ...
  end

  def send_pay(pay_check)
    # ...
  end
end

# lib/pay_roll/pay_check.rb
#
class PayRoll::PayCheck
  # ...
end

## Rails application

# app/controllers/pay_day_controller.rb
# Yes, this would make more sense to be run in a scheduled job, but wanted to show
# an example of services used in a Rails controller
#
class PayDayController < ApplicationController
  def create
    PayRoll::PayDayService.new.execute
    redirect_to :back, :notice => "Pay day has been successfully completed"
  end
end

# models/employee.rb
# The data in DCI
#
class Employee < ActiveRecord::Base
  scope :active, where(:active => true)
end