In particular, we consider three measures based on n-gram matching: BLEU-2 (Papineni et al., 2002), ROUGE (Lin, 2004), and observed.
this is in line with Downing (1977), who argues that novel (i.e., not yet lexicalised) noun-noun compounds can be built by speakers on the fly based on a temporary, implicit relationship tying the two nouns, e.g., 'the guy taking a picture with a camera'.