We gauge how best to select source sentences by exploring different similarity metrics.
(i) LCS calculates the longest common subsequence between a candidate source sentence and the reference sentence; (ii) VSM represents sentences using the vector space model and calculates the cosine similarity between the two sentence vectors; (iii) Smatch (Cai and Knight, 2013) calculates the F-score of AMR concepts between the candidate and reference sentences; (iv) Concept Coverage selects source sentences to maximize the coverage of AMR concepts of the reference sentence.