@Book{kobert2012einsteigerseminar,
  author = {Kobert, Thomas},
  title  = {Das Einsteigerseminar HTML},

  year   = {2012},
  number = {},
  url    = {http://deposit.d-nb.de/cgi-bin/dokserv?id=3528771&prov=M&dok_var=1&dok_ext=htm},

  const  = {\ text}
}