There is a wide range of new applications that stress the need for business process models that are able to handle imprecise data. This paper studies the underlying modelling and analysis issues. It uses as formal model to describe process behaviours a labelled transitions system in which transitions are guarded by conditions defined over a probabilistic database and presents an approach for testing probabilistic simulation preorder in this context. A complexity analysis reveals that the problem is in 2-exptime, and is exptime-hard, w.r.t. expression complexity while it matches probabilistic query evaluation w.r.t. data-complexity.