Irfan Ul Haq Adrian Paschke Erich Schikuta Harold Boley Rule-Based Workflow Validation of Hierarchical Service Level Agreements. 96-103 2009 GPC Workshops http://doi.ieeecomputersociety.org/10.1109/GPC.2009.25 conf/gpc/2009w db/conf/gpc/gpc2009w.html#HaqPSB09