Discourse Level Factors for Sentence Deletion in Text Simplification
Table 7: Fraction of sentences that contain the explicit discourse connectives. Arrows indicate significance (p<0.05) using the Wilcoxon ranked test; ↑: higher presence among deleted sentences than the kept ones; ↓: lower.
['[EMPTY]', 'Middle Kept', 'Middle Deleted', 'Elementary Kept', 'Elementary Deleted']
We first compare how often discourse connectives appear in deleted vs. kept sentences in the original version, and the relation senses they signal: contingency, comparison, expansion, or temporal, following the PDTB taxonomy. We did not conduct analysis on fine-grained levels of the taxonomy due to label sparsity. Deleted sentences are in general significantly more likely to have a connective, a potential signal that the sentence is complex (i.e., has more than one clause). This is especially evident for the elementary level in that this holds for all relations. Deleted sentences are significantly less likely to have temporal ones in the middle level. For both levels, document characteristics matter more than position, especially in the middle level task. One reason could be that middle level simplification is based more on content, while editors tend to shorten the whole texts in elementary level simplification by dropping sentences near the end of an article. Another reason could be the noise introduced during automatic alignment, for example, potential noise in partial match, that could render signals from discourse relations uninformative during training.