class Paper
  include DataMapper::Resource
  property :id, Serial
  property :name, String
  has n, :authors, :class_name => "Person", :through => Resource
  has n, :citations
  has n, :papers, :through => :citations
end

class Citation
  include DataMapper::Resource
  belongs_to :citing_paper, :class_name => "Paper", :child_key => [:cited_paper_id]
  belongs_to :cited_paper, :class_name => "Paper", :child_key => [:cited_paper_id]
end