@article{foo1999,
  title={Buchtitel},
  author={Doe, John},
  keywords={book},
  journal={International Journal of Nonsense},
  year={1999}
}

@online{bar1999,
  author = {Ford, Rebecca},
  keywords={internet},
  title  = {Earthquake: Twitter Users Learned of Tremors
            Seconds Before Feeling Them},
  date   = {2011-08},
  url    = {http://www.hollywoodreporter.com/news/earthquake-twitter-users-learned-tremors-226481}
}