BNL: The Problem - Update

The concept behind this 'chapter' is basically the same as the last time I put it on my blog; however, the example is largely new. As always, feedback welcome.

Business Natural Languages: Introduction
Business Natural Languages: The Problem
Business Natural Languages: The Solution
Business Natural Languages: DRY code, DAMP BNL
Business Natural Langauges: Moving to the web and multiple contexts
Business Natural Languages: Limitations
Business Natural Languages: Common Pieces

The Problem
To demonstrate the value in implementing a Business Natural Language we will start with an existing ruby application and then introduce a simple Business Natural Language. This approach should provide a good example of how to include a Business Natural Language in an application.

For the sample application imagine you've been contracted to replace a payroll calculation system for a consulting company. The consulting company chose to custom develop the software for calculating payroll because of the varying compensation packages. They have given you profiles of 2 employees and the business rules required to generate compensation.

Profiles:
John Jones
compensate $2500 for each deal closed in the past 30 days
compensate $500 for each active deal that closed more than 365 days ago
compensate 5 percent of gross profits if gross profits are greater than $1,000,000
compensate 3 percent of gross profits if gross profits are greater than $2,000,000
compensate 1 percent of gross profits if gross profits are greater than $3,000,000

Jackie Johnson
compensate $3000 for each deal closed in the past 30 days
compensate $800 for each active deal that closed more than 365 days ago
compensate 5 percent of gross profits if gross profits are greater than $1,000,000
compensate 5 percent of gross profits if gross profits are greater than $2,000,000

The application need only be run monthly; therefore, manual execution of the application is acceptable. The existing application is executed at the command line and the results are displayed to the screen. The payroll department records the application results in another system that is outside of the scope of your work. A preprocess is run to put monthly sales information in a known location in an agreed upon format, this is also outside the scope of your work. The only input files we will need for our sample application are jjones.yml and jjohnson.yml.

File: jjones.yml

employee: jjones
deals_this_month: 7
year_old_deals: 2
gross_profit: 1400000

File: jjohnson.yml

employee: jjohnson
deals_this_month: 12
year_old_deals: 1
gross_profit: 2200000

The SalesInfo class currently reads the sales data and exposes it via class method calls that are handled by method_missing.

File: sales_info.rb

require 'yaml'

class SalesInfo

  @employee_sales_info = Dir['*.yml'].collect do |filename|
    YAML::load(File.open(filename))
  end
  
  def self.method_missing(sym, *args)
    hash = @employee_sales_info.find { |hash| hash.value?(sym.to_s) }
    super if hash.nil?
    EmployeeInfo.new(hash)
  end

  class EmployeeInfo
    attr_reader :employee, :deals_this_month, :year_old_deals, :gross_profit
    def initialize(hash)
      hash.each_pair do |key, value|
        instance_variable_set :"@#{key}", value
      end
    end
  end

end

The ruby file that executes the current payroll process is very straightforward:

File: process_payroll.rb

require 'jjones'
require 'jjohnson'

puts "John Jones compensation: #{JJones.calculate}"
puts "Jackie Johnson compensation: #{JJohnson.calculate}"

Each employee ruby file is also fairly straightforward. They contain the logic to calculate compensation, expressed as ruby.

File: jjones.rb

require 'sales_info'

class JJones
  def self.calculate
    total = SalesInfo.jjones.deals_this_month * 2500
    total += SalesInfo.jjones.year_old_deals * 500
    profit = SalesInfo.jjones.gross_profit
    total += profit * 0.05 if profit > 1000000
    total += profit * 0.03 if profit > 2000000
    total += profit * 0.01 if profit > 3000000
    total
  end
end

File: jjohnson.rb

require 'sales_info'

class JJohnson
  def self.calculate
    total = SalesInfo.jjohnson.deals_this_month * 3000
    total += SalesInfo.jjohnson.year_old_deals * 800
    profit = SalesInfo.jjohnson.gross_profit
    total += profit * 0.05 if profit > 1000000
    total += profit * 0.05 if profit > 2000000
    total
  end
end

The existing application produces the following output.

John Jones compensation: 88500.0
Jackie Johnson compensation: 256800.0

The code produces accurate results; however, the code has limited ability to easily be extended for new employees. Additionally, employees are required to re-negotiate their compensation structure every year. Following a compensation change a programmer must be involved to change the employees logic. The current process is clearly sub-optimal