A candidate phrase, typically a sequence of nouns and adjectives, is selected as a keyphrase if (1) it includes one or more of the top-ranked candidate words<cite> (Mihalcea and Tarau (2004)</cite> , Liu et al. (2009b) ), or (2) the sum of the ranking scores of its constituent words makes it a top scoring phrase (Wan and Xiao, 2008) .