Complex and flexible business processes are critical not only because they are difficult to handle, but also because they often tend to loose their intelligibility. Verifying compliance of complex and flexible processes becomes therefore a fundamental requirement. We propose a framework for performing compliance checking of process execution traces w.r.t. expressive reactive business rules, tailored to the MXML meta-model. Rules are mapped to Logic Programming, using Prolog to classify execution traces as compliant/non-compliant. We show how different rule templates, inspired by the ConDec language, can be easily specified and then customized in the context of a real industrial case study. We finally describe how the proposed language and its underlying a-posteriori reasoning technique have been concretely implemented as a ProM analysis plug-in.