In this paper, we describe the so-called precedence relation method. This method may be used to derive truncation models which produce bounds for the relevant performance measures of a given Markovian queueing system. The truncation models may be defined such that the size of the state space is flexible in the sense that it depends on the choice of certain truncation parameters. The models which we obtain in this way are called flexible bound models and they may lead to efficient procedures for the determination of the performance measures of interest. The precedence relation method will be demonstrated for the symmetric shortest queue system.