“…Kernels for discrete objects have been studied by Haussler [14], and many graph kernels have been proposed after that. There are three major groups in graph kernels: kernels based on walks and paths [9,20,10,3,42,43], kernels based on limited-size subgraphs [16,36,21], and kernels based on subtree patterns [25,35,15]. Among them, random walk based kernels have been proved to be one of the most successful methods [5,4,34].…”