Classifying strokes into different categories is an essential preprocessing step in the automatic document understanding process. To tackle this task, it is crucial to integrate different types of contextual information. Previous methods which are based on conditional random fields or recurrent neural networks have some limitations in model capacity or computational cost. In this paper, we propose a novel framework based on graph attention networks to solve this problem, which casts the stroke classification problem into the node classification problem in a document graph. In the graph, each node represents a stroke and the edges are built from temporal and spatial interactions between strokes. Combined graph convolution with attention mechanisms to dynamically aggregate features from the neighborhood, our model is very flexible to control the message passing routine between different nodes and therefore has strong capability learning context-aware features. We perform comparison experiments on the IAMonDo dataset and experimental results demonstrate the superiority of our approach.

In this paper, we propose an efficient and robust algorithm for graph-based transductive classification. After approximating a graph with a spanning tree, we develop a linear-time algorithm to label the tree such that the cut size of the tree is minimized. This significantly improves typical graph-based methods, which either have a cubic time complexity (for a dense graph) or O(kn2) (for a sparse graph with k denoting the node degree). Furthermore, our method shows great robustness to the graph construction both theoretically and empirically; this overcomes another big problem of traditional graph-based methods. In addition to its good scalability and robustness, the proposed algorithm demonstrates high accuracy. In particular, on a graph with 400,000 nodes (in which 10,000 nodes are labeled) and 10,455,545 edges, our algorithm achieves the highest accuracy of 99.6% but takes less than 10 seconds to label all the unlabeled data.