FUML13 — The fUML subset should include central buffer nodes and data stores

Specification: Semantics of a Foundational Subset for Executable UML Models, FTF Beta 3 (ptc/10-03-14)

Unlike pins, the tokens in central buffer nodes and data stores (which are kind of central buffer node) are not consumed when they are accessed. This allows a value to be, e.g., stored in a data store and used repeatedly in a loop that is modeled directly using flows rather than using a loop node. It is more common to create loops using flows than structured nodes when drawing graphical activity diagrams, and fUML should provide reasonable execution semantics for such models using central buffer nodes and data stores.

Add central buffer nodes and data stores

Actually, the tokens in a central buffer node are withdrawn from the central buffer node when offers for them are accepted. On the other hand, values on tokens in data store nodes do effectively "persist". This makes data store nodes the important ones to include. However, since data store nodes are kinds of central buffer nodes, including data store nodes implies the need to also include central buffer nodes.

CentralBufferNode is in the IntermediateActivities package in UML 2.4.1, which is already included in the fUML subset. DataStoreNode, however, is in the CompleteActivities package, which, heretofore, has not been part of the fUML subset. Therefore, in order to add DataStoreNode, it is necessary to add a new subclause for the CompleteActivities package, even though only one metaclass is to be included from that package. Further, this package must be added to the L3 merge for fUML.