A comprehensive study of features and algorithms for URL-based topic classification
E. Baykan, M.H. Henzinger, L. Marian, I. Weber, ACM Transactions on the Web 5 (2011).

On near-uniform URL sampling
M.H. Henzinger, A. Heydon, M. Mitzenmacher, M. Najork, Computer Networks 33 (2000) 295–308.