Risk Analysis

The FTA diagram sample "Fault tree analysis - Insulin delivery system" was redesigned from the illustration of "CMSI 641: Introduction to Software Engineering. Design of Critical Systems. B.J. Johnson. 2005. Loyola Marymount University".
"Another way of assessing hazards is using fault tree analysis. In this process, each of the identified hazards is covered by a detailed analysis to find out what might cause it. Either inductive or deductive reasoning is applied. In the case of software hazards, the usual focus is to determine faults that will cause the system to fail to deliver a system service, such as a monitoring system. A "fault tree" is constructed to link all the possible situations together, to help identify the interrelationships of the failures, which modules may cause them, and what "trickle-down effects" there might be. Here is an example of a fault tree, as applied to the Insulin delivery system from Sommerville...
Note that this tree is only partially complete, since only the potential software faults are shown on the diagram. The potential failures involving hardware, such as low battery, blood monitor or sensor failure, patient over-exertion or inattention, or medical staff failure are noticeable by their absence.
The fault tree and safety specification processes are two ways of helping with system risk assessment tasks. Once the risks are identified, there are other assessments that need to take place. First, the likelihood of the risk occurrance must be assessed. This is often quantifiable, so numbers may be assigned based on things like MTBF, latency effects, and other known entities. There may be other non-quantifiable contributors to the risk likelihood, however, such that these must be assessed and estimated by experts in the domain. (Don't short-change this process when dealing with critical systems!) Finally, the risk assessment must include the severity of the risk, meaning an estimation of the cost to the project in the event the risk item actually does occur. "Cost to the project" means all associated costs, including schedule delays, human injury, damage to hardware, corruption of data, and so on."
[myweb.lmu.edu/ bjohnson/ cmsi641web/ week15-2.html]
The FTA diagram example "Fault tree analysis - Insulin delivery system" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Fault Tree Analysis Diagrams solution from the Engineering area of ConceptDraw Solution Park.

"Process Decision Program Chart (PDPC).
A useful way of planning is to break down tasks into a hierarchy, using a tree diagram. The PDPC extends the tree diagram a couple of levels to identify risks and countermeasures for the bottom level tasks. Different shaped boxes are used to highlight risks and identify possible countermeasures (often shown as 'clouds' to indicate their uncertain nature). The PDPC is similar to the Failure Modes and Effects Analysis (FMEA) in that both identify risks, consequences of failure, and contingency actions; the FMEA also rates relative risk levels for each potential failure point." [Seven Management and Planning Tools. Wikipedia]
The Risk diagram (process decision program chart, PDPC) determines the risks when corrective action is not performed correctly. Also, it helps develop descriptions for preventive actions at the level of execution.
The Risk diagram (PDPC) template for the ConceptDraw PRO diagramming and vector drawing software is included in the solution "Seven Management and Planning Tools" from the Management area of ConceptDraw Solution Park.