## article.rb

class Article
  include DataMapper::Resource

  property :id,          Integer, :serial => true
  property :url,         String,  :nullable => false, :length => 255, :format => /http:\/\//
  property :body,        Text

  has n, :matches
  has n, :keywords, :through => :matches
end

## keyword.rb

class Keyword
  include DataMapper::Resource

  property :id,         Integer,  :serial => true
  property :keyword,    String,   :nullable => false

  has n, :matches
  has n, :articles, :through => :matches

end

## matches.rb

class Match
  include DataMapper::Resource

  property    :id,      Integer, :serial => true
  belongs_to  :article
  belongs_to  :keyword
  property    :weight,  Integer

end