While a machine learning approach is used in (Gildea and Jurafsky, 2000) to determine general semantic roles, we used a simple rule-based traversal of the parse tree instead, which could also reliably determine the generic agent and patient role of a sentence, and this suffices for our current purpose.
for a given noun phrase candidate ¥ ¡ , the following groups of features are used: Verb of Agent NP (VAg) When ¢ ¡ is an agent in a sentence, each of its associated verbs is a VAg feature.