Probabilities on an Activity

SysML 1.6 defines many uses for probabilities in systems modeling.  For example, probabilities may be applied to value properties of a block (see Distributed Properties of a «block») and can also be applied to control flows and parameter sets on an activity diagram.  When applied to value properties, the «distributedproperty» stereotype is used and when applied to a parameter set, the «probability» stereotype is used.

According to the SysML specification, “when the «probability» stereotype is applied to edges coming out of decision nodes and object nodes, it provides an expression for the probability that the edge will be traversed. These shall be between zero and one inclusive, and add up to one for edges with same source at the time the probabilities are used.”  When the «probability» stereotype is applied to output parameter sets, “it gives the probability the parameter set will be given values at runtime. These shall be between zero and one inclusive, and add up to one for output parameter sets of the same behavior at the time the probabilities are used.”

The «probability» stereotype is applied to the control flows exiting the decision node to model the likelhood of each decision being made.

In the example, the control flows exiting the decision node both have the «probability» stereotype applied.  This allows the actual probability to be stated.  In the example, the likelihood of making decision A is 10% whereas the likelihood of making decision B is 90%.

References:

Object Management Group (2018) OMG Systems Modeling Language Version 1.6. Needham, MA: OMG. Para 11.1.13, 11.3.2.7, Table 11-2.