OPTION double InitialNode

Gallery
Tutorial
TRAIL: Webel's ultimate guide to Systems Modeling Language (v1) with MagicDraw/Cameo
Section
01:04: UML Behavior: Activities quick start
Topic level
ESSENTIAL
UML keywords
Activity
Activity Diagram
InitialNode
JoinNode
ControlFlow
Keywords
Slide kind
UML Activity Diagram
Using more than one InitialNode is another way to address the initialisation problem illustrated in a previous slide:
UML-2.5.1: 'An Activity may have more than one InitialNode.'
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But beware that - while an Activity may have more than one InitialNode - a StateMachine may only have one initial Pseudostate in each Region:
UML-2.5.1: 'There can be at most one initial Vertex in a Region.'
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ExecutableNode has implicit fork
Notes
Snippets (quotes/extracts)
  [UML-2.5.1] An Activity may have more than one InitialNode.
  [UML-2.5.1] An InitialNode shall not have any incoming ActivityEdges, which means the InitialNodes owned by an Activity will always be enabled when the Activity begins execution and a single control token is placed on each such InitialNode when Activity execution sta
  [UML-2.5.1] The outgoing ActivityEdges of an InitialNode must all be ControlFlows. The control token placed on an InitialNode is offered concurrently on all outgoing ControlFlows.
  [UML-2.5.1] As an ActivityNode may be the source for multiple ActivityEdges, the same token can be offered to multiple targets.
  [UML-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 ...).
  [UML-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.
  [UML-2.5.1] 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.
  [UML-2.5.1] Tokens offered to a ForkNode are offered to all outgoing ActivityEdges of the node. If at least one of these offers is accepted, the offered tokens are removed from their original source and the acceptor receives a copy of the tokens.
Related slides (includes other tutorials)
INCORRECT InitialNode no implicit fork
CORRECT InitialNode explicit fork
Related slides (backlinks, includes other tutorials)
ExecutableNode has implicit fork
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