Control Structure Diagram

Understanding Control Structure (CS) Diagrams in STPA

• CS Diagrams are fundamental in constructing and visualizing the control structure and relationships between components.
• They help in understanding control actions of each component and identifying unsafe or potentially inadequate control actions.

Creating a Control Structure Diagram

1. To create a CS Diagram, navigate to [Diagram] → [STAMP/STPA] and select [Control Structure Diagram].
   
2. The new diagram will be added to the [STAMP/STPA Model] facet.
   
   

Adding Components

• Components represent Controllers and Controlled processes.
• Double-click on the diagram to create a new Component, which will be added both to the diagram and the tree view under the [STAMP/STPA Model] facet

You can also create multiple Components at once by copying and pasting text.

Nesting Components

Create a hierarchical structure by nesting components.
This can be done by double-clicking an existing Component or dragging one component onto another.

Creating a Dedicated CS Diagram for a Component

For more detailed analysis, create a specific CS Diagram for a component by right-clicking on it and selecting [Create Diagram] → [Control Structure Diagram].

Adding Process Models

1. Right-click on a Component and select [Process Model Compartment Visibility].
   
   
   
2. “<process model>” will appear in the Component. Right-click again and select [Add Process Variable] to define processes.
   
   
   These can also be added in the property view (left-bottom pane of Astah).
   

Creating Links

To connect a link to represent a relationship between the models, use a link.
Hover a Component and click a mini arrow icon in solid line, then click the target model.

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.

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.

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.

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.