Sunday, 28 April 2013 22:36

Chapter 9 - Process Evolution and Instance Migration

9.1. Similarities and Differences between Ad-hoc Changes and Propagated Type Changes

Both the ad-hoc change of a single process instance, and the propagation of a process type change to corresponding process instances, constitute dynamic process changes. Discuss their commonalities and differences.


9.2. Process Model Evolution and Instance Migration

Fig. 9.23 shows the evolution of process model S: Activity I is deleted and activity E is serially inserted between activities B and F, resulting in process model S'. Consider now process instances I1, I2, and I3 running on S as depicted on the left-hand side of Fig. 9.24. For each of these instances check whether or not it may migrate to the new process model S' presuming state compliance as a basic corrections notion. If Ik migrates to S', draw the process instance and its state resulting from this migration (use the templates on the right hand-side of Fig. 9.24 for this). Otherwise, give a reason why migration is not possible.

Fig. 9.23 Evolution of a Process Model


9.3. Conflicting Changes at the Process Type and Process Instance Level

Consider the evolution of process model S to S' as depicted in Fig. 9.25A: a control dependency is added indicating that activity D needs to be completed before activity B may be enabled. Furthermore consider the two process instances I1 and I2 shown in Fig. 9.25B. Both I1 and I2 were derived from S, but are now running on instance-specific process models SI1 and SI2, respectively, due to previous ad-hoc changes. For example, SI1 was derived from S by adding activity X after activity A and before activities B and D.

To which of the two process instances may the process type change be propagated? Give an explanation referring to Definition 9.3.


9.4 Disjoint and Overlapping Process Type and Process Instance Changes

Consider the evolution of process model S to S' as depicted in Fig. 9.26A: Activity C is deleted (leading to the concomitant deletion of the two gateway nodes) and activities X between A and B) and Y(between B and D) are added.

  • Consider the unbiased process instances I1 and I2 from Fig. 9.26B that were created from S. For each process instance decide whether it may migrate to S'.Draw the resulting process instance graph if migration is possible.
  • Consider the biased process instances I3, I4, and I5 from Fig. 9.26C which were created from S. For each of these process instances categorize its instance-specific bias in relation to the process type change τt depicted in Fig. 9.26A. Decide whether or not the respective process instance may be migrated to the new process model version. If migration is possible, provide the process instance graph and instance bias resulting afterwards.

Fig. 9.24 Migration of Related Process Instances

Fig. 9.25 Evolution of a Process Model and Related Biased Process Instances


9.5. Coping with Non-compliant Process Instances

Fig. 9.26 Evolution of a Process Model and Related Process Instances


  • Discuss the pros and cons of the five migration strategies suggested in the context of non-compliant process instances (cf. Section 9.4).
  • Consider the process model evolution from S to S' as depicted in Fig. 9.4 and the related process instance I3. In the given scenario, I3 is non-compliant with S' and is therefore not directly migratable to S'. Which of the five migration strategies can be applied in the given context in order to relink I3 to S' in the end, i.e., to migrate I3 to S', while preserving the soundness of I3? For each applicable migration strategy show the result after the migration of I3.

Fig. 9.4 Controlled Migration of Process Instances


9.6 Process Model Evolution versus Process Model Refactorings

Compare process model evolution and process model refactoring. Discuss commonalities and differences.


9.7 Process Model Smells and Process Model Refactorings

Consider the process model depicted in Fig. 9.27. What process model smells can you identify in this model? How would you refactor the process model to improve the quality of the model? Justify your proposal.

Fig. 9.27 A Process Model Containing Process Model Smells

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