UML22 — StructuredActivityNode [UML 2.1.1]

StructuredActivityNode, based on both common sense and its semantics, requires input and output pins. However StructuredActivityNode::input and StructuredActivityNode::output, both inherited from Action are derived unions and so cannot be used directly. StructuredActivityNode::result is a concrete property but has a special meaning.

What is needed is some solution that subsets StructuredActivityNode::input and StructuredActivityNode::output but can be used to describe input and output pins of StructuredActivityNode.

The semantics of StructuredActivityNode does, indeed, talk specifically about pins on such nodes. Further, having pins on StructuredActivityNodes is assumed as being allowed in and is required by the Java to UML activity model mapping in the Foundational UML specification. The submitter is correct, however, that the abstract syntax model itself does not seem to explicitly support this.