<http://schema.org/topics>
"acquisition,Apps and Software,Facebook,jan koum,MAUs,Mobile,monthly active users,one billion users,Social Media,Uncategorized,WhatsApp?,mark zuckerberg"^^<http://www.w3.org/2001/XMLSchema#string>
<http://mashable.com/2014/02/19/whatsapp-reach-one-billion-users/>