Plugin Configuration

CHESS-SBA has a set of configuration parameters, which can be set from a property page under the CHESS group. To access it select Window / Preferences / CHESS / StateBased Preferences from the menu.

DEEM Server

One of the main parameters for the analysis execution is the location of the DEEM Simulator server.

Parameter	Default	Description
DEEM Server Host	rclserver.dsi.unifi.it	Address of the DEEM Server.
DEEM Server Port	5903	Port on which the DEEM Simulator server is listening.
Connection Timeout	60	Timeout for the connection to the DEEM Server, specified in seconds.

Simulator Configuration

The DEEM Simulator can be tuned to improve the accuracy of its results or to speedup the evaluation of a particularly complex model. This is done by altering the stopping conditions of the simulation, that is, the conditions under which the simulator will consider the computed metrics good enough.

Parameter	Default	Description
Minimum Batches	1000	Minimum number of measure samples that the simulator will collect.
Maximum Batches	1000000	Maximum number of measure samples that the simulator will collect.
Confidence Interval (Relative)	0.1	Interval (relative to the measure's computed mean) in which the real value of the measure is likely to fall.
Confidence Level	0.99	Requested probability that the real value of the measure will fall in the given confidence interval.
Display Update Interval	100	Number of samples after which the display is updated. Bigger values reduce the overhead in displaying the progress, but increase the interval at which progress display is updated.
Measure update interval	100	Number of samples after which the measure is updated. This is the minimum amount of samples that are run between two subsequent checks of stopping conditions.
Simulation Seed	6657	Seed used to initialize the simulation. Different seeds yield different simulation paths.

Meaning of Parameters

Such parameters are common across discrete-event simulators of different kind. An interpretation of the meaning of parameters based of default values is:

• The simulator will stop and provide a result only when, for every computed measure:
  • 99% samples of the evaluated measure fall within an interval of ±1% from the computed mean, and
  • at least 1000 samples have been collected,
• or
  • more than 1000000 samples have been collected,
• and this check is performed every 100 samples.

Tweaking

Default values have been selected to work well in most situations. However, depending on your model structure and numerical values, they might need to be tweaked to improve the quality of results or reduce the time needed to execute the analysis.

Tweaking of discrete-event simulator parameters typycally involve:

• Increasing the confidence level or decreasing the confidence interval, to get more accurate results.
• Increasing the minimum number of batches when the events you would like to measure are very rare. Otherwise the simulator may never experience them, and provide you with strange unexpected results (e.g. a zero value that should be something else).
• Decrease the minimum batches for the simulation to end earlier. Beware that the same comment about rare events apply: if too few batches are collected, results may be incorrect!
• Decrease the maximum batches to force the simulation to stop after a given amount of time. In this case, typically, results do not converge with the requested precision, i.e., the requested confidence interval and confidence level are not respected.

Parametric Execution

CHESS-SBA supports the parametric execution of the analysis, i.e., with some numerical values that are read from an external file. The following attributes in the property page are used to configure this feature.

Parameter	Default	Description
Parametric: Parameters File	parameters.txt	The input file for parametric execution, where parameters are stored.
Parametric: Results File	results.txt	The output file for parametric execution, where results are stored.
Parametric: Interval	60	The interval between two subsequent periodic runs, if periodic execution is enabled.
Parametric: Periodic Runs	false	Whether periodic execution is enabled or not.