Classic supervised learning makes the closed-world assumption, meaning that
classes seen in testing must have been seen in training. However, in the
dynamic world, new or unseen class examples may appear constantly. A model
working in such an environment must be able to reject unseen classes (not seen
or used in training). If enough data is collected for the unseen classes, the
system should incrementally learn to accept/classify them. This learning
paradigm is called open-world learning (OWL). Existing OWL methods all need
some form of re-training to accept or include the new classes in the overall
model. In this paper, we propose a meta-learning approach to the problem. Its
key novelty is that it only needs to train a meta-classifier, which can then
continually accept new classes when they have enough labeled data for the
meta-classifier to use, and also detect/reject future unseen classes. No
re-training of the meta-classifier or a new overall classifier covering all old
and new classes is needed. In testing, the method only uses the examples of the
seen classes (including the newly added classes) on-the-fly for classification
and rejection. Experimental results demonstrate the effectiveness of the new
approach.

本文提出一种元学习方法来解决开放世界学习中增量学习和未知类别拒绝的问题。该方法只需要训练一个元分类器，而不需要重新训练元分类器或一个新的分类器来涵盖所有老和新类别。实验证明了该方法的有效性。