Safety concept diagrams represent the concept of safety architecture designs.
The specification is formed by Safety Concept Notation Study Group.

SCDL Sample Diagram
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You can create a Requirement by directly double-clicking on a diagram.

SG, FSR, TSR, HWSR, SWSR, and NFSR beside the R box are the stereotypes. Please choose which stereotype you want before creating a Requirement by double-clicking.

You can also create a Requirement by copying and pasting texts.
Create Requirements by text

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By double-clicking on the top-right corner, you can set ASIL(Automobile Safety Integrity Level) to the requirement individually.

Learn more about ASIL on this page.

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Requirement Group

You can create a Requirement Group by choosing one with a stereotype you’d like on the toolbar (SM or MF), and click on a diagram.
Requirement Group

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Constraint Paring

When you want to associate a Requirement with a Requirement Group, use [Constraint Pairing].
Choose the [Constraint Pairing] from the toolbar and click a Requirement and Requirement Group.
Constraint Pairing

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Requirement Group paring

You can make a pair of two Requirement Groups by using [Requirement Group Pairing].
Choose the [Requirement Group Pairing] from the toolbar and click a Requirement group and another.
Requirement Group Pairing


In order to make a pair of Requirement Groups, one of the Requirement Group needs to be linked to a Requirement which has ASIL A or higher.

Use [Constraint Pairing] to connect a Requirement Group and a Requirement.

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Elements can represent a system, subsystem, components…etc. where you can drag Requirements inside to represent the inclusive relationships.
Create Elements

You can create another element inside an existing element to create sub-element. In this case, the outside element should mean it is the system boundary.
Create Sub Elements in SCDL Diagram

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Interaction is an arrow line you can create from one Requirement to another to represent a transfer of information, signal or message.
To draw an interaction, have a mouse over a Requirement diagram and click on a small arrow, then click to a target Requirement.
Create Interactions between Requirements

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System Boundary Interaction

When you want to represent input from outside of the system or output to outside of the system which you won’t depict on the diagram, you should use System Boundary Interaction.
Choose a fat arrow from the toolbar and click wherever you want it to start and click on a target Requirement or click on a source Requirement and click to where ever you want the arrow to point.
System Boundary Interaction

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You can represent the decomposition using Requirements, Requirement Group and Requirement Group pairing.

SCDL Decomposition

For example, regarding the design shown above, there is a possibility of malfunction that could occur from wrong transmission of the “Send Position” request or its loss signal. So we can design the SM-001 (Safety Mechanism 001) that we implement dual detection systems and add priority judgement as below:

Create a “Intended Function” Requirement Group and associate it with “FR-100” Requirement with Constraint-pairing.
Also, create another Requirement Group and let it associated with newly added “FSR-001” and “FSR-002” requirements that are included in the new SM-001.

You can decompose by pairing these two Requirement Groups with “Requirement Group Pairing”.

  1. Add a Requirement Group Pairing between “Intended Function” and ”SM-001”. [Select ASIL] dialog opens.
  2. Select ASIL that you’d like to assign to Requirements in each Requirement Group.
    Assign ASIL
  3. Now create a Requirement that all the requirements in both Requirement Groups do not disturb other requirements. And add the Requirement to the Requirement Group with [Constraint Pairing].
    Safety Concept Diagram Decomposition

This is how decomposition works.
After decomposing, you can still change the Requirement’s ASIL and names.