1. A method for operating a computer system, with processor and memory, comprising: obtaining a process model, the model having (a) a directed graph with nodes that are associated with process steps, and with edges that are associated with a flow of execution from predecessor steps to successor steps, (b) boolean pre-conditions and post-conditions, such that a post-condition of a predecessor step of the predecessor steps can be the pre-condition for execution of a successor step of the predecessor step, and (c) boolean variables to determine logical values of the conditions; detecting dependencies between variables that are required to determine the logical values of the pre-conditions, splitting the model into sub-models so that dependent variables remain within sub-models, and checking the flow of execution with pre-conditions and post-conditions for possible combinations of the dependent variables for each sub-model separately.