@Book{jannach2011recommender,
  author = {Jannach, Dietmar},
  title  = {Recommender systems : an introduction},

  year   = {2011},
  number = {},
  url    = {http://www.amazon.de/Recommender-Systems-Introduction-Dietmar-Jannach/dp/0521493366/ref=sr_1_1?ie=UTF8&qid=1356099943&sr=8-1},

  const  = {\ text}
}