Transition

A Transition is a type of node within a scenario.

Transitions can usually have :

• one or more upstream places.
• one (for state machines) or more downstream places.

Transitions can usually have :

• Zero or mutiple Sensor functions
• Zero or mutiple Effector functions
• A Token merge function
• A Token assign function
• A priority

Transitions can fire if :

• All upstream places contain a token
• There is no Sensor function or all the Sensor functions are valid

When a transition fires it sequentially:

• Consumes and merges (see Token Merge) all upstream places tokens
• Merges all sensors event contexts in an array of contexts. Each sensor context data path is prefixed with it's order number (i.e. the first sensors context data is in EventContext.0.xxxxx)
• Sequencially runs all the Effector functions (see Effector)
• Assigns a token in every downstream place (see Token Assign) (note that if at least one of these downstream place contains a token, an error occurs)

Transitions also contain a priority value, defaulted to zero. A higher priority transition gets to be checked before lower priority transitions. For more details on the order in which all functions of a transition are called, see Safe Petri Network.