Control Structure (CS) Diagram is a one of the first steps to building a STPA. You use a CS diagram to construct and visualize the control structure and relationships between the Components that will help you understand the control actions of each component and identify the unsafe or potential inadequate control actions of the system.
Control Structure Diagram

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How to create a Control Structure Diagram

To create a diagram,

  1. Go to [Diagram] – [STAMP/STPA] and choose [Control Structure Diagram].
    Create control structure diagram
  2. Then a diagram will be created and added in the [STAMP/STPA Model] box.
    Control Structure Diagram in tree
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Components

In order to represent Controllers and Controlled processes, use Components.
You can directly double-click on a diagram to create a Component.
A new Component will be added to a diagram and also to the tree view under [STAMP/STPA] model box.
New Components

You can also copy and paste the text to create multiple Components at once.
Create Components by text

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Nest Components

You can create a hierarchical structure of components by nesting one to another.
You can directly double-click on an existing Component or just drag a Component to an existing one.
Nested Components

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Create another CS Diagram under a Component

You can also create another Control Structure Diagram dedicated to one specific Component to define more detailed about the Component. To create one, right-click on a Component and select [Create Diagram] – [Control Structure Diagram].
Create another Control Structure Diagram

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Process Models

In order to add a process model which determine control actions,

  1. Right-click on a Component and click [Process Model Compartment Visibility] from the pop-up menu.
    Add Process Model
  2. <process model> appears in the Component. Now right-click and select [Add Process Variable] to define processes.
    Add process variable

    This can be done in the property view of the Component (left-bottom pane of Astah).
    Define process model
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Creating a Link

To connect a link to represent a relationship between the models, use a link to connect them.
Also, you need to create a link first in order to create the control actions.
Hover a Component and click a mini arrow icon in solid line, then click the target model.

Adding a link from the controller to the controlled process

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Control Actions

To add a Control Action which is what the the controller provides to control some process and to enforce constraints on the behaviour of the controlled process, hover a Link and click [CA] icon.

Adding Control Actions in STPA

Providing Condition

In order to add a providing condition, click a Control Action in the diagram and open the property view(left-bottom pane of Astah) and enter it in the [Providing Condition] field.
Providing Condition

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Feedback

To add a Feedback that provides information to the controllers about how effectively the constraints are being satisfied, create a Feedback link first, hover the Feedback link and click [FB] icon.

Adding feedback from the controlled process to Controller

Providing Condition

In order to add a providing condition, click a Feedback in the diagram and open the property view(left-bottom pane of Astah) and enter it in the [Providing Condition] field.
Providing Condition for Feedback