component.rb

class Component < ActiveRecord::Base
  has_many :components

  #this is the 'other side' of the has_many :components statement
  belongs_to :component

  has_one :sub_component
end

create_component.rb

class CreateComponent < ActiveRecord::Migration
  def self.up
    create_table :components do |t|
      #need this here to allow components to reference each other
      t.references :component
      t.integer :elevation_index
      t.string  :oreintation

      t.timestamps
  end

  def self.down
    drop_table :components
  end
end

create_sub_component.rb

class CreateSubComponent < ActiveRecord::Migration
  def self.up
    create_table :sub_components do |t|
      t.references :component
      # t.references :sub_component #don't need this because sub_components aren't referencing each other
      t.string :sub_component

      t.timestamps
  end

  def self.down
    drop_table :sub_components
  end
end

sub_component.rb

#Inherits from AR::Base rather than Component because we don't really want STI here (which is what you get if you inherit from a model)
class SubComponent < ActiveRecord::Base
  belongs_to :component
end