appointment.rb

class Appointment < ActiveRecord::Base
  has_many :steps
  has_many :roles, through: :steps
  has_many :events, through: :roles
end

event.rb

class Event < ActiveRecord::Base
  belongs_to :role
  
  # access appointment by doing event.role.step.appointment
end

role.rb

class Role < ActiveRecord::Base
  has_many :events
  belongs_to :step
  
  # access appointment by doing role.step.appointment
end

routes.rb

# /appointments/
# /appointments/1/
# /appointments/new
resources :appointments do 

  # /steps/1
  # /appointments/1/steps/new
  # /steps/1/edit
  resources :steps, shallow: true do
  
    # /steps/1/roles/new
    # /roles/1/edit
    # /roles/1
    resources :roles, shallow: true do
    
      # /roles/1/events/new
      # /roles/1/events/
      # /events/1
      # /events/1/edit
      resources :events, shallow: true
    end
  end
end

step.rb

class Step < ActiveRecord::Base
  has_many :roles
  has_many :events, through: :roles
  belongs_to :appointment
  
  #access appointment by doing step.appointment
end