It is worth noting that besides the approach difference, these two works employ rather different resources and settings in their evaluation, making it impossible to directly compare their performance.
while Plank and Moschitti (2013) only use the path-enclosed trees induced from the constituent parse trees as the representation for relation mentions, Nguyen and Grishman (2014) include a rich set of features extracted from multiple resources such as constituent trees, dependency trees, gazetteers, semantic resources in the representation.