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Deriving Analyses from Design
To further analyze the effects of a cyber attack on high level system functions and functional safety an FMEA analysis and / FTA might be used. Based on the information stored in the system model an FMEA can be derived from a system element. Failure modes and failure nets (FMEA) can be used to derive an FTA.
Deriving FMEA
The FMEA structure can be derived by right-click on a system element in model explorer or diagram:
Right-click on the system element representing the item.
Choose Derive>FMEA
Select folder (optional).
Enter a name.
Define additional root element (optional) (to be implemented).
Click Finish.
An additional root element in step 3 might be needed in FMEA as an object containing failure effects.
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Use the buttons in upper right corner of the window to toggle visibility of certain FMEA content. Please refer to page new FMEA to complete FMEA structure as needed.
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Synchronization between FMEA and UML Model
FMEA and UML model are bidirectionally synchronized:
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Continue editing your FMEA structure. System elements, functions and malfunctions can be added to the structure as needed. Once the structure is completed, create action groups on causes of failure, define prevention and detection actions and create form sheets. Please refer to page new FMEA for further details.
Deriving an FTA
There are several options for using model information for FTA:
Create a new FTA document on a malfunction.
Add a malfunction and its causes at a lower level to an existing FTA document by dragging and dropping.
Drag a single malfunction on a gate in an existing FTA document.
Creating a New FTA Document on a Malfunction (to be implemented)
A new FTA document can be created by right-clicking on a malfunction in the Model Explorer or a diagram:
Right-click on a malfunction representing the top event of the fault tree (root).
Choose Derive>FTA.
Select folder (optional).
Enter a name.
Enter mission time (optional).
Click Finish.
An FTA document is created and visible in the FTA folder in repository view. The selected malfunction is the root element of the fault tree. Due to the OR-semantics of connected malfunctions in design and FMEA (failure net) all malfunctions on a certain level are connected to a next higher-level malfunction via OR gates.
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Edit and complete the structure of the FTA.
Adding a Fault Tree to an Existing FTA Document by Dragging and Dropping
A malfunction and its causes on lower level can be added as a fault tree to an existing FTA document by dragging and dropping. Ensure that the Link with Editor button is activated in model explorer view. Locate the malfunction of interest in model explorer and drag it into an FTA document. You can either drop it into an empty document so that the malfunction becomes the root of the fault tree, or you drop it on a gate to add the fault tree below that gate. In either case click on Add fault tree in the dialog that appears.
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Add or Replace a Gate in an Existing FTA Document
In addition, you can create or replace a gate by dragging and dropping of a malfunction from the Model Explorer on a gate in an FTA document. Either click on Replace or Create new gate in the Add fault tree dialog.
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FTA =>UML: Malfunctions added to the failure tree using the FTA editor are listed in in Package FTA in model explorer
UML =>FTA: If changes are made to system design relevant for the failure tree this is displayed by the highlighted Synchronize FTA … button in the upper right corner of the FTA editor (to be implemented). The FTA Synchronizer wizard allows for selecting elements to add to FTA.
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