%0 Generic %D 2006 %T On the branching complexity of P systems %A Gabriel Ciobanu %A Gheorghe Paun %A Mario J. Pérez-Jiménez %C Amsterdam, Holanda %I IOS Press %K decidability %K descriptional complexity %K Membrane computing %K non-determinism %N 1-2 %P 27-36 %U http://portal.acm.org/citation.cfm?id=1231163 %V 73 %X We consider two complexity parameters related to the graph of reachable configurations of a given P system, namely the outdegree as a measure of the degree of non-determinism, and the indegree as a measure of the degree of confluence. These parameters can be defined for both the generative and the accepting mode of using a P system. We investigate here these parameters in what concerns hierarchies and decidability issues. We prove that all hierarchies have only two levels and that all considered decidability problems have a negative answer.