Most of existing studies dealing with comparable corpora look for parallel data at the sentence level (Zhao and Vogel, 2002;Utiyama and Isahara, 2003;Munteanu and Marcu, 2005;Abdul-Rauf and Schwenk, 2011).
the degree of parallelism can vary considerably, from noisy parallel texts, to quasi parallel texts (Fung and Cheung, 2004).