334 Chapter 12 Natural laNguage INterfaCe: QuestIoN aNswerINg system
because the creation of an index is limited by the speed of the parser and
because sophisticated linguistic representations were not amenable to large-
scale indexing. The current generation of question answering systems that
employ NLP alleviate performance problems by delaying linguistic analysis
until the corpus has been narrowed down to a small set of candidate docu-
ments or passages. The MURAX system is an early example of such an ap-
proach. After retrieving a set of candidate documents, the system parses both
the questions and the passages, and attempts matching at the relationship
level.
However, a drawback of this two-step paradigm is low recall: If the