The aligner computes for each word pair across Q and S (i) a semantic similarity score sim W ∈ [0, 1] using PPDB-a large database of lexical paraphrases developed using bilingual pivoting (Ganitkevitch et al., 2013).
it allows three different levels of similarity: 1 if the two words or their lemmas are identical, a value ppdbSim ∈ (0, 1) if the word pair is present in PPDB (the XXXL database) 2 , and 0 otherwise.