To determine whether a noun phrase instance NP i should be extracted as a filler for an event role, GLACIER computes the joint probability that NP i : (1) appears in an event sentence, and (2) is a legitimate filler for the event role.
gLACIER is designed for noun phrase extraction and, mathematically, its decisions are based on the following joint probability: where S NP i is the sentence containing noun phrase NP i .