Activity Structured Activity Node

Structured Activity Node

A Structured Activity Node contains a nested Activity graph. It groups steps behind one node in the containing Activity and gives the nested graph its own Initial, Input, and optional Output nodes. This is the UML structured activity node pattern; it does not create a separately addressed Activity behavior instance.

flowchart LR
    outer(Parent Activity)
    outer --> input["Input boundary"]
    subgraph nested["Structured Activity"]
        input --> normalize(Normalize)
        normalize --> output["Output boundary"]
    end
    output --> next(Parent continuation)

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Mermaid approximation: this diagram shows the model's routing, not a complete UML Activity notation. Rounded boxes represent actions; edge labels identify token types or guards. Input/Output boxes name Stateflows boundary APIs, not UML final nodes or a claim that UML uses these box labels. Mermaid does not model pins, activity parameters, or expansion regions natively.

Passing data through the boundary

The parent sends tokens to the structured node through its incoming object flow. Inside the node, AddInput routes selected input types to nested nodes. To return a value, connect a nested producer to OutputNode, declare AddOutput(), and connect the structured node's outgoing object flow to a parent node.

.AddInitial(initial => initial.AddControlFlow("ReadAmount"))
.AddAction(
    "ReadAmount",
    async c => c.Output(125m),
    node => node.AddFlow<decimal>("Normalize"))
.AddStructuredActivity("Normalize", nested => nested
    .AddInput(input => input.AddFlow<decimal>("Round"))
    .AddInitial(initial => initial.AddControlFlow("Round"))
    .AddAction(
        "Round",
        async c => c.Output(decimal.Round(
            c.GetTokensOfType<decimal>().Single(), 2)),
        node => node.AddFlow<decimal, OutputNode>())
    .AddOutput()
    .AddFlow<decimal>("RecordAmount"))
.AddAction("RecordAmount", async c =>
    await ledger.RecordAsync(
        c.GetTokensOfType<decimal>().Single(), c.CancellationToken))

The nested definition also supports actions, control nodes, event actions, and further structured nodes. Its configuration and active nodes are scoped under the containing node. A structured node can remain active across event processing; use Behavioral Groups when referring to state-machine-embedded behaviors, which are separate behavior instances rather than nested Activity nodes.

See Input Node, Output Node, and Parallel Activity Node.