Data-centric approaches to business process management, in general, no longer require specific activities to be executed in a certain order, but instead data values must be present in business objects for a successful process completion. While this holds the promise of more flexible processes, the addition of the data perspective results in increased complexity. Therefore, data-centric approaches must be able to cope with the increased complexity, while still fulfilling the promise of high process flexibility. Object-aware process management specifies business processes in terms of objects as well as their lifecycle processes. Lifecycle processes determine how an object acquires all necessary data values. As data values are not always available in the order the lifecycle process of an object requires, the lifecycle process must be able to flexibly handle these deviations. Object-aware process management provides operational semantics with built-in flexible data acquisition, instead of tasking the process modeler with pre-specifying all execution variants. At the technical level, the flexible data acquisition is accomplished with process rules, which efficiently realize the operational semantics.