A taxonomy and review of generalization research in NLP

The ability to generalize well is one of the primary desiderata for models of natural language processing (NLP), but what ‘good generalization’ entails and how it should be evaluated is not well understood. In this Analysis we present a taxonomy for characterizing and understanding generalization research in NLP. The proposed taxonomy is based on an extensive literature review and contains five axes along which generalization studies can differ: their main motivation, the type of generalization they aim to solve, the type of data shift they consider, the source by which this data shift originated, and the locus of the shift within the NLP modelling pipeline. We use our taxonomy to classify over 700 experiments, and we use the results to present an in-depth analysis that maps out the current state of generalization research in NLP and make recommendations for which areas deserve attention in the future. With the rapid development of natural language processing (NLP) models in the last decade came the realization that high performance levels on test sets do not imply that a model robustly generalizes to a wide range of scenarios. Hupkes et al. review generalization approaches in the NLP literature and propose a taxonomy based on five axes to analyse such studies: motivation, type of generalization, type of data shift, the source of this data shift, and the locus of the shift within the modelling pipeline.