As discussed in § 7, prior work has generally treated tagging the PPCEME as a problem of domain adaptation, with a post-processing stage to map deterministically between the tagsets.
we train on the Penn Treebank (PTB) corpus of 20th century English (Marcus et al., 1993), and then evaluate on the PPCEME test set, using a mapping between the PPCHE and PTB tagsets defined by Moon and Baldridge (2007).