<https://www.realizingprogress.com/2013/02/foursquare-fur-die-tourismusbranche-ein-interview-mit-holger-luedorf-von-foursquare/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.realizingprogress.com/2013/02/foursquare-fur-die-tourismusbranche-ein-interview-mit-holger-luedorf-von-foursquare/>