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Monday, 29 April 2013 08:14

Chapter 12 - Constraint-based Process Models

12.1. Specifying Constraint-based Process Models: 

Denali National Park offers visitors a wide range of outdoor opportunities. Table 12.3 depicts the activities which are available for planning your trip to Denali.

Table 12.3 Activities
Visit Visitor Center Short Hike
Flightseeing White Water Rafting
Full Day Rafting 4-Hour Scenic Rafting
Obtain Permit Backpacking
Take Bus from Wonderlake Take Bus to Wonderlake
Bus Tour Wonderlake (Roundtrip) Denali Natural History Tour

 When planning the trip the following constraints need to be considered:

  • All activities except for Visit Visitor Center can be executed at most once.
  • Only one of the following activities can be executed: White Water Rafting, Full Day Rafting or 4-Hour Scenic Rafting.
  • Backpacking requires a permit.
  • Only one of the two activities Denali Natural History Tour and Bus Tour Wonderlake (Roundtrip) may be executed.
  • Since activity Backpacking starts at Wonderlake you need to take the Bus to Wonderlakedirectly before performing that activity. Directly after the hike you have to take the Bus from Wonderlake to get back.

Create a constraint-based process model which correctly reflects the above described constraints. For working on this exercise you can use the DecSerFlow Modeler of the Cheetah platform which you can download from the book web site.

12.2. Understanding Constraint-based Process Models (1): 

Fig. 2.3 depicts a constraint-based process model of how to treat fractures,

  • Trace <Examine Patient,Prescribe Medication, Perform Sling> is supported.
  • If there is activity Prescribe Fixation in a trace there must be Perform X-ray before.
  • Trace <Examine Patient, Prescribe Medication, Perform Sling, Prescribe Medication, Prescribe Fixation> is supported.
  • At any point during process execution Prescribe Medication can be executed; i.e., for every process instance I in state Running,Prescribe Medication is always enabled.
  • Trace <Examine Patient, Perform X-ray, Perform Sling, Prescribe Fixation, Perform Surgery> is supported.

12-3
Fig. 12.3 Choice Constraints

 

12.3. Understanding Constraint-based Process Models (2): 

Fig. 12.24 depicts a constraint-based process model consisting of six activities and ten constraints. Which of the following statements are true?

12-24
Fig. 12.24 Constraint-based Process Model S1

  • If C occurs in a trace, it must be directly preceded by B.
  • Trace <F,A,B,C,F> is supported by S1.
  • Trace <A,B,D,E,A,A> is supported by S1.
  • At any point during process execution A can be executed, i.e., for every process instanceI in state Running, A is always enabled.
  • The number of occurrences for Dis greater or equal the number of occurrences for E in every complete trace.
  • The number of occurrences for A is greater or equal than the number of occurrences for F in every complete trace.
  • If there is a C, a trace must not contain an E.

 

12.4. Understanding Constraint-based Process Models (3): 

Fig. 12.25 depicts a constraint-based process model consisting of seven activities and twelve constraints. Which of the following statements are true?

  • Trace <R,D,B> is supported by S2.
  • If there is a N there must not be an F afterwards.
  • Trace <R,P,F,K,F> is supported by S2.
  • At any point during process execution R can be executed; i.e., for every process instance I in state Running, R is always enabled.
  • The number of occurrences of R is greater or equal the number of occurrences of B in every complete trace.
  • Trace <R,B,K,D,N> is supported by S2.

 

12-25
Fig. 12.25 Constraint-based Process Model S2

 

12.5. Constraint-based and Pre-specified Process Models (1):

  • For the constraint-based process model from Fig. 12.26 create a pre-specified process model showing the same behavior.
  • Compare pre-specified and constraint-based process models. Describe commonalities and differences as well as advantages and disadvantages of the different approaches.

12-26Fig. 12.26 Constraint-based Process Model S3

 

12.6. Evolving Constraint-based Process Models Supported by Test-driven Modeling: 

To get some hands-on experience on how to evolve a constraint-based process model supported by Test-driven Modeling visit the book website and follow the instructions related to this exercise. Given an initial constraint-based process model and a list of requirements you will be asked to conduct a list of changes to the model.

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