Therefore, term P(T)/P({tw∈T}) is determined mainly by the word order in T and not influenced by the popularity of title words in T. As already discussed in the introduction section, the old framework for title generation allows all the words in the document equally participate in selecting title words and therefore, the final choice of title words may be influenced significantly by the common words in the document which have nothing to do with the content of the document.
we suggest a solution to this problem by introducing a hidden state called 'information source' which is able to sampled the important content words from the original document.