Evaluation Metrics Despite differences in the exact definitions, the majority (e.g., Hsu et al., 2018; Celikyilmaz et al., 2018;<cite> Narayan et al., 2018b</cite>; Chen and Bansal, 2018; Peyrard and Gurevych, 2018) agree on both or either one of two broad quality definitions: coverage determines how much of the salient content of the source document is captured in the summary, and informativeness, how much of the content captured in the summary is salient with regards to the original document.