The FBI thing is a terrible/brilliant idea, discerning meaning from Natural Language/ Social Media posts is an exercise in futility. There are too many complexities starting with the fact that people will simply state the exact opposite to their view point. However, catching on to large scale events like a riot happening is actually pretty easy because you have the weight of averages through word frequency on your side. However, this is almost trivially easy to do with twitter's api and keyword searching so lord knows why the FBI are advertising the fact they want someone to develop a system for them. Twitters trending topics basically does it already.