5.5.2.1.2. Decision Node

Decision Node

A Decision Node selects outgoing flows according to guards. A token decision evaluates object-flow guards for each token; a control decision evaluates control-flow guards without application data. Both are UML decision nodes, drawn as diamonds. A decision routes along eligible guarded flows; an else flow is the fallback when no guarded flow is selected.

flowchart LR
    start((●)) --> price(Read price)
    price -->|decimal| choose{Decision}
    choose -->|token >= 100| review(Manual review)
    choose -->|else| auto(Auto-approve)

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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. Mermaid does not provide native Activity node semantics.

Token decision

Specify the token type on AddDecision<TToken>. Each guard receives the candidate token as c.Token.

.AddAction(
    "ReadPrice",
    async c => c.Output(125m),
    node => node.AddFlow<decimal, DecisionNode<decimal>>())
.AddDecision<decimal>(decision => decision
    .AddFlow("ManualReview", flow => flow
        .AddGuard(async c => c.Token >= 100m))
    .AddElseFlow("AutoApprove"))
.AddAction("ManualReview", async c => await review.QueueAsync(c.CancellationToken))
.AddAction("AutoApprove", async c => await approval.ApproveAsync(c.CancellationToken))

The decision forwards matching tokens through the selected object flows. It does not execute application action code itself. If flows need to change the token type, configure an outgoing-flow transformation.

Control decision

Use AddControlDecision when the branch depends on state or another source rather than an incoming token:

.AddControlDecision(decision => decision
    .AddFlow("Approved", flow => flow.AddGuard(async c =>
        await c.Behavior.Values.GetOrDefaultAsync("approved", false)))
    .AddElseFlow("Rejected"))

The default Decision Node option includes ImplicitJoin; configure node options if a different incoming-flow activation rule is required. See Control Flow, Data Flow, and Implicit Fork and Join.