Linguistically motivated syntactic units such as noun phrases (Zhai, 1997), head-modifier pairs (Fagan, 1987;Strzalkowski et al., 1996) and subjectverb-object triples (Katz and Lin, 2003) have also been integrated in information retrieval.
it has been argued that NLP and especially deep syntactic analysis is still too brittle and ineffective (Katz and Lin, 2003).