Question Answering in the QBTE Model 1 involves directly classifying words w i in the document into answer words or non-answer words.
given input x (i) for w i , its class label is selected from among {I, O, B} as follows: I: if the word is in the middle of the answer word sequence; O: if the word is not in the answer word sequence; B: if the word is the start word of the answer word sequence.