This means that an Activity model in which non-determinacy occurs may be subject to timing issues and race conditions. It is the responsibility of the modeler to avoid such conditions in the construction of the Activity model, if they are not desired. Source Unified Modeling Language 2.5.1
If a token is offered to multiple ActivityNodes at the same time, it shall be accepted by at most one of them, but exactly which one is not completely determined by the Activity flow semantics. Source Unified Modeling Language 2.5.1
However, the same token can only be accepted at one target at a time (unless it is copied, whereupon it is not the same token, see ForkNodes ... and ExecutableNodes ...). Source Unified Modeling Language 2.5.1
As an ActivityNode may be the source for multiple ActivityEdges, the same token can be offered to multiple targets. Source Unified Modeling Language 2.5.1
ExecutableNodes actually carry out the desired behavior of an Activity. If an ExecutableNode has incoming ControlFlows, then there must be tokens offered on all these flows that it accepts before beginning execution. Source Unified Modeling Language 2.5.1
ObjectNodes hold object tokens accepted from incoming ObjectFlows and may subsequently offer them to outgoing ObjectFlows (with a modeler-specified exception for ControlFlows, see isControlType for ObjectNodes ...). Source Unified Modeling Language 2.5.1
ControlNodes act as “traffic switches” managing the flow of tokens across ActivityEdges. Tokens cannot “rest” at ControlNodes (with exceptions for InitialNodes and ForkNodes ...). Source Unified Modeling Language 2.5.1
ControlFlows are used to explicitly sequence execution of ActivityNodes, as the target ActivityNode cannot receive a control token and start execution until the source ActivityNode completes execution and produces the token. Source Unified Modeling Language 2.5.1
An ExecutableNode may also consume and produce data, but it must do so through related ObjectNodes (Actions use Pins for this purpose ... Source Unified Modeling Language 2.5.1
An ExecutableNode is an ActivityNode that carries out a substantive behavioral step of the Activity that contains it. Source Unified Modeling Language 2.5.1
Generally, the ControlNodes and ObjectNodes in an Activity are largely there to control the sequencing and to manage the flow of data between the ExecutableNodes of the Activity. Source Unified Modeling Language 2.5.1
An ExecutableNode is a kind of ActivityNode that may be executed as a step in the overall desired behavior of the containing Activity. Source Unified Modeling Language 2.5.1
When the «rate» stereotype is applied to an activity edge, it specifies the expected value of the number of objects and values that traverse the edge per time interval, that is, the expected value rate at which they leave the source node and arrive at ... Source OMG Systems Modeling Language (SysML) 1.6
