A PDTB-Styled End-to-End Discourse Parser
Table 3: Results for identifying the Arg1 and Arg2 subtree nodes for the SS case under the GS + no EP setting for the three categories.
['[EMPTY]', 'Arg1  [ITALIC] F1', 'Arg2  [ITALIC] F1', 'Rel  [ITALIC] F1']
We next evaluate the performance of the argument extractor. The last column shows the relation level F1 which requires both Arg1 and Arg2 nodes to be matched. We only show the results for the GS + no EP setting to save space. As expected, Arg1 and Arg2 nodes for subordinating connectives are the easiest ones to identify and give a high Arg2 F1 of 97.93% and a Rel F1 of 86.98%. We note that the Arg1 F1 and Arg2 F1 for coordinating connectives are the same, which is strange, as we expect Arg2 nodes to be handled more easily. The error analysis shows that Arg2 spans for coordinating connectives tend to include extra texts that cause the Arg2 nodes to move lower down in the parse tree. For example, “… and Mr. Simpson said he resigned in 1988” contains the extra span “Mr. Simpson said” which causes the Arg2 node moving two levels down the tree. As we discussed, discourse adverbials are difficult to identify as their Arg1 and Arg2 nodes are not strongly bound in the parse trees. However, as they do not occupy a large percentage in the test data, they do not lead to a large degradation as shown in the last row.