<http://schema.org/topics>
"digg,Facebook,Google,infographics,linkedin,MySpace,pinterest,plaxo,Social Media,tumblr,Twitter,Uncategorized,WAYN,yelp"^^<http://www.w3.org/2001/XMLSchema#string>
<http://mashable.com/2012/08/02/social-network-data-infographic/>