BPMN simulation - result metrics¶
This article explains the metrics of the multiple case simulation‘s results.
We use the following simplified vacation request handling process to produce example metrics.
A vacation request handling process
We have one Team Lead resource available at a cost of 60€ per hour. The execution costs are:
- 1€ per activity, plus
- 60€ *
#hours of human work needed to execute the activities.
The execution times are:
- 10 minutes for Assess vacation request,
- 5 minutes for Explain rejection.
Consequently, the activity Assess vacation request costs 11€ and takes 10 minutes. The activity Explain rejection costs 6€ and takes 5 minutes.
The process has two flow variants:
- variant 1: vacation is granted,
- variant 2: vacation is rejected.
Variant 1 occurs in 80% of the cases, costs 11€ and takes 10 minutes. Variant 2 occurs in 20% of the cases, costs 17€ and takes 15 minutes.
The simulation tool calculates average, minimum, maximum, and total costs. The tool determines all cost types based on the simulation result. If you run a simulation of our example process with exactly one case that takes process variant 2, each cost amounts to 17€.
The simulation tool calculates average, minimum, maximum and total cycle times. As for the costs, the simulation tool determines the cycle times based on the simulation result. If you run a simulation of our example process with exactly one case that takes process variant 2, each cycle time amounts to 15 minutes.
The total cycle time can exceed the simulation time span. This can happen for two reasons:
- Your resources can’t handle cases fast enough and process instances ‘pile up’.
- The cases that occur in the last hours/minutes of your simulation time frame exceed this frame before they are completed.
The resource consumption lists the consumed time and the workload for each process resource.
The consumed time is the total time a resource spends on executing activities.
For example, if your simulation result contains 80 cases of variant 1 and 20 cases of variant 2, the Team Lead‘s resource consumption is
80 x 10 minutes + 20 x 15 minutes = 1100 minutes.
The workload is the percentage of the available time a resource is occupied with executing activities.
Given the example above, a simulation time frame of one week and a resource availability of 40 hours per week, the workload of the Team Lead resource is
1100 / (40 * 60) = 37% (approx.) (given no case exceeds the simulation time frame).
Bottlenecks & waiting times¶
A bottleneck occurs when a resource’s limited availability increases the waiting times of cases. In our example, a bottleneck occurs at Assess vacation request as soon as a new case starts while the Team Lead is still handling a previously started case. Then, adding additional Team Leads will reduce waiting times and cycle times.
Waiting times describe how long cases are idle because no resource is available to execute the current activity. In our example scenario, only one resource is available to handle process activities. Consequently, waiting times occur when a new case is started before all previous cases have been terminated.