This is a hard problem -- there's a bunch of research in NLP on it, where it's sometimes called temporal tagging. HeidelTime is a system that does this; some e

This is a hard problem -- there's a bunch of research in NLP on it, where it's sometimes called temporal tagging. HeidelTime is a system that does this; some examples on their webpage, https://code.google.com/p/heideltime/ https://code.google.com/p/heideltime/