Initial Node

Overview

The Initial Node represents the starting point of an Activity or Structured Activity Node. It is a special type of Node that has no incoming Flows and is automatically activated when the Activity/Structured Activity Node executes.

An Initial Node consists of:

• Name, uniquely identifying the Initial Node within the Activity,
• Outgoing Control Flows, passing Control Token to the next Nodes.

Definition

In UML, an Initial Node is represented as a filled circle:

flowchart

initial@{ shape: circle, label: " " }
initial --> action1
action1(SomeAction)
initial --> action2
action2(AnotherAction)

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Equivalent Stateflows notation of an Initial Node:

Lambda style

    /* fragment of Activity definition */
    .AddInitial(b => b
        .AddControlFlow("SomeAction")
        .AddControlFlow("AnotherAction")
    )
    .AddAction("SomeAction",
        async c => {
            /* logic for the action */
        }
    )
    .AddAction("AnotherAction",
        async c => {
            /* logic for the action */
        }
    )

Typed style

    public class SomeAction : IActionNode
    {
        public async Task ExecuteAsync()
        {
            /* logic for the action */
        }
    }

    public class AnotherAction : IActionNode
    {
        public async Task ExecuteAsync()
        {
            /* logic for the action */
        }
    }

    /* fragment of Activity definition */
    .AddInitial(b => b
        .AddControlFlow<SomeAction>()
        .AddControlFlow<AnotherAction>()
    )
    .AddAction<SomeAction>()
    .AddAction<AnotherAction>()

Using lambda style and typed style doesn't change anything for Initial Node - it is not referenced by name nor type, simple AddInitial() call declares it.

Usage

The Initial Node is the entry point of an Activity and Structured Activity Nodes and is executed when Activity / Structured Activity Node is initialized. It is not mandatory though: Activity can define no logic on initialization, but react to incoming Tokens using Input Node or to incoming Events using Accept Event Action Nodes.