Ataytis Assurance · Event Tree Analysis
Event tree validation
The rules an event tree is checked against and their severity, the messages they produce and how to fix them, and the advisories.
Rules
| Rule | Severity |
|---|---|
| Exactly one initiating event | Error |
| Nothing leads to the initiating event | Error |
| Nothing follows an outcome | Error |
| A pivotal event or branch point has branches | Error |
| Branch probabilities from 0 to 1 | Error |
| The branches of a split add up to 1 | Error |
| The initiating frequency is 0 or more | Error |
| No cycles | Error |
| A pivotal event has more than one branch | Warning |
| Every branch of a split has a probability, or none does | Warning |
| Branches of the same kind at a split have different Order values | Warning |
| Node and relationship types are recognised | Warning |
| Every node is joined to the tree | Warning |
None of these stops the tree drawing. A missing Node ID, Node type or Relationship type mapping does.
Messages and fixes
| Message | Fix |
|---|---|
| Map the required Relationship type. | Map a Relationship Type column. Blank cells in it are fine. Node type gives the same message when it is not mapped. |
| Initiating Event is missing. | Add a row with Node Type Initiating Event. |
| Initiating Event occurs 2 times. | Keep one initiating event per tree. Put separate trees under separate Diagram IDs. |
| An initiating event starts the tree, so nothing may lead to it. Remove the incoming connection, or make this a pivotal event. | Clear Connected Node ID on the initiating event's row. If every outcome is reported too, the table names the next node: change Reads as on the Data Mapping tab. |
| An outcome ends its sequence, but this one leads on to another event. Remove the onward connection, or change this node's type to a pivotal event. | Remove the rows that follow the outcome, or change its Node Type. |
| Nothing leaves this pivotal event, so the sequences through it never reach an outcome. Add its branches, or make it an outcome if the sequence ends here. | Add rows for its branches, or change it to an outcome. |
| Only one branch leaves this pivotal event, so nothing is being decided at it. Add the other branch, or connect the sequence straight through if there is no choice here. | Add the missing branch. |
| A branch probability of 98 is outside 0 to 1. Every sequence through this branch is quantified from it. | Enter probabilities as fractions: 0.98, not 98. |
| The branches leaving this event sum to 1.0100, not 1. They are meant to be exhaustive and mutually exclusive, so every downstream frequency is wrong until they complete. | Correct the probabilities on the rows of that split's branches. |
| One branch of 2 leaving this event has no probability, so every sequence through it is left uncounted while the rest of the tree is quantified. Supply the missing value, or remove the others to keep the tree qualitative. | Add the missing probability, or remove all of that split's probabilities. |
| An initiating frequency of -1 is not a finite value of zero or more. | Correct Frequency on the initiating event's row. |
| Two branches of the same kind leave this event with the same order, so which is drawn first depends on the order the rows arrive in. Give them different values. | Give the branches different Order values. |
| "Partial" is not a recognised relationship type. Map it to one under Data Mapping, or the rows using it stay unrecognised. | Map the value under Relationship values on the Data Mapping tab. The same value is also reported as Partial is not supported by this diagram mode. |
| The graph contains a directed cycle that is invalid for this mode. | A row names a later node as the one before it. Check Connected Node ID. |
| The diagram contains 2 disconnected components. | Some rows are not joined to the tree. Check Connected Node ID. |
Names and numbers in these messages come from your data, so yours will differ.
Advisories
| Advisory | Severity | Raised when |
|---|---|---|
| No frequency is mapped for the initiating event, so sequences show a path probability rather than a frequency. | Information | The initiating event has no Frequency. |
| 1 of 5 sequences cannot be quantified because a branch on the path has no probability. | Information | A branch on a sequence's path has no probability. |
Turn advisories off by setting Diagram → Validation → Advisory diagnostics to Hide advisories. The rules above are still checked.