@Phdthesis{bogers2009recommender,
  author = {Bogers, Toine},
  title  = {Recommender Systems for Social Bookmarking},

  year   = {2009},
  number = {},
  url    = {http://ilk.uvt.nl/~toine/phd-thesis/},

  const  = {\ text}
}
@Phdthesis{jschke2011formal,
  author = {Jäschke, Robert},
  title  = {Formal concept analysis and tag recommendations in collaborative tagging systems},

  year   = {2011},
  number = {},
  url    = {http://www.worldcat.org/search?qt=worldcat_org_all&q=9783898383325},

  const  = {\ text}
}