<http://schema.org/topics>
"amazon,Android,Android App,e-reading,Google,google ebooks,iPad,ipad app,iPhone,iPhone Apps,kindle,kobo,news,nook"^^<http://www.w3.org/2001/XMLSchema#string>
<http://mashable.com/2010/12/06/google-ebooks-iphone-android-ipad-web/>