Schema Evolution in Process Management Systems

Continuously arising new trends in information technology and developments at the (e-business) market let companies crave for automated business process support. Process management systems offer the promising possibility to (electronically) define, control, and monitor business processes.
However, if this technology shall be applicable in practice it must be possible to change running business processes even at runtime. Basically, such process changes can take place at two levels - the process type level
and the process instance level. If a process type is modified a new version of the respective process type schema is created. Then, at minimum, the process instances running according to the old process type schema version must be able to finish without being disturbed. However, this simple versioning approach is only sufficient for short-running business processes. For long-running ones like, for example, car leasing contracts or medical treatment processes which may last from 3 up to 5 years, it must be possible to apply the process type changes to the collection of running process instances as well, but without causing inconsistencies or errors in the sequel.
Apart from process schema evolution and change propagation a flexible process management system must also enable instance-specific (ad-hoc) changes, for example, if exceptional situations occur. If then a process type change takes place the challenging question arises how to adequately deal with the interplay of process type and process instance changes.