We add sequential operations to the categorical algebra of weighted and
Markov automata introduced in [L. de Francesco Albasini, N. Sabadini and R.F.C. Walters,
arXiv:0909.4136]. The extra
the algebra permits the description of hierarchical systems, and ones with
evolving geometry. We make a comparison with the probabilistic automata of
Lynch et al. [SIAM J. Comput.37 (2007) 977–1013].