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Workflow Management Kap. 4. Analyzing Workflows Wil van der Aalst has copyrights to almost all figures in the following slideshow made by Lars Frank.

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“Soundness” analysis can prevent logical errors:

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Soundness property:

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Unbounded and never ending loop error: A petri net is bounded when there is an upper limit for tokens. A petri net is safe when the upper limit for tokens is one for all places = Bounded by value one.

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Soundness property proof: If a transition is replaced by a sound workflow, then the resulting workflow is also sound.

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Examples of Sound nets:

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Example of Sound proof:

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Why is there no proof for the soundness property?

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Techniques to analyze workflows: (About the structure of the workflow. For example soundness) (About attribute values and management of the workflow)

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Is this process correct? (In analyzing the workflow you should use the knowledge learned from the previous example)

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Dangling tasks error = Petri net is not live: A petri net is live when all tasks can be loaded.

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Deadlock illustration where both Trans1 and Trans2 want to lock(låse) Object1 and Object2:

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Fairness property: The fairness property says that if a task potentially can be executed, then it will be executed sooner or later. Does the workflow have a logical error if task2 is a “marriage” that produce “families”?

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Hanging cases before termination:

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Petri-net analysis :

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Reachability graph without cycles: Reachability graph with reachable states:

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Reachability graph with cycles: (red1,green1,yellow1,safe,red2,green2,yellow2,safe) Green Both red Yellow Green

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Some petri nets has Place invariants: Place invariants = Constant calculated as the weightet sum of the tokens in each place. Example: man +woman + 2 * couple = 7

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Performance analysis: Computer simulation is the repeated execution of a process where choices are made upon various probability distributions. A Markov chain is a reachability graph with the probability of transition added to it.

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The following slides illustrate 6 different basic workflow constructions for integrating 2 activities:

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Example 1. Sequential:

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Example 2. Parallel:

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Example 3. Compose:

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Example 4. Flexible resources:

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Example 5. Triage:

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Example 6. Priority:

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Example 7. Results of analysis:

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Guidelines for workflow design:

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Calculate capacity and utilization: If x is the execution time for a task then 1/x is the capacity and N/x the utilization when N cases are executed.

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A general queue model:

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A queue model with even distribution for arrivals:

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A queue model with negative exponential distribution for arrivals:

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Properties of simulation:

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Prove the soundness of the coupled e- commerce workflow?

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Which e- commerc e model will you re- commend in practice?

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End of session Thank you !!!

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Petri net Work flow for global E-commerce transactions where the stocks are in the locations of the different suppliers. OR split

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Sub- Petri net of activity 2 AND split OR split AND join

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Exercise in quantitative analysis:

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