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.
To create a diagram,
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.
You can also copy and paste the text to create multiple Components at once.
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.
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].
In order to add a process model which determine control actions,
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.
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.
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.
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.
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.