class Segmentlink < ActiveRecord::Base
  belongs_to :child, :class_name => 'Segment', :foreign_key => 'child_seg_id'
end

class Segment < ActiveRecord::Base
  has_many :children, :class_name => 'SegmentLink', :foreign_key => 'child_seg_id'
  has_one :parent, :class_name => 'SegmentLink', :foreign_key => 'parent_seg_id'
end