... 1: An example on question retrievalmost information retrieval models, such as vectorspace model (VSM) (Salton et al., 1975), Okapi model (Robertson et al., 1994), language model (LM) (Ponte ... ranking model frameworkfor question retrieval in which different modelsare incorporated as features because the phrase-based translation model cannot be interpolatedwith a unigram language model ... When µ1= 1, the retrieval model is basedon phrase-based translation model for the question part. When µ2= 1, the retrieval model is based onphrase-based translation model for the answer part.3.3...