Leveraging Class Hierarchies with Metric-Guided Prototype Learning
Authors: Vivien Sainte Fare Garnot, Loic Landrieu
Keywords: hierarchical classification, prototypical networks
Abstract: In many classification tasks, the set of classes can be organized according to a meaningful hierarchy. This structure can be used to assess the severity of confusing each pair of classes, and summarized  under the form of a cost matrix which also defines a finite metric. We propose to integrate this metric in the supervision of a prototypical network in order to model the hierarchical class structure. Our method relies on jointly learning a feature-extracting network and a set of class representations, or prototypes, which incorporate the error metric into their relative arrangement in the embedding space. We show that this simultaneous training allows for consistent improvement of the severity of the network's errors with regard to the class hierarchy when compared to traditional methods and other prototype-based strategies. Furthermore, when the induced metric contains insight on the data structure, our approach improves the overall precision as well. Experiments on four different public datasets—from agricultural time series classification to depth image semantic segmentation—validate our approach.