Strategy synthesis for Markov decision processes and branching-time logics

Abstract

We consider a class of finite 1 1/2-player games (Markov decision processes) where the winning objectives are specified in the branching-time temporal logic qPECTL* (an extension of the qualitative PCTL*). We study decidability and complexity of existence of a winning strategy in these games. We identify a fragment of qPECTL* called detPECTL* for which the existence of a winning strategy is decidable in exponential time, and also the winning strategy can be computed in exponential time (if it exists). Consequently we show that every formula of qPECTL* can be translated to a formula of detPECTL* (in exponential time) so that the resulting formula is equivalent to the original one over finite Markov chains. From this we obtain that for the whole qPECTL*, the existence of a winning finite-memory strategy is decidable in double exponential time. An immediate consequence is that the existence of a winning finite-memory strategy is decidable for the qualitative fragment of PCTL* in triple exponential time. We also obtain a single exponential upper bound on the same problem for the qualitative PCTL. Finally, we study the power of finite-memory strategies with respect to objectives described in the qualitative PCTL. © Springer-Verlag Berlin Heidelberg 2007.