Write the branch logic
In this fictional service, success requires resolver R and either branch A or branch B: R AND(A OR B). All start available. A failure affects only the named component; there are no hidden links. Two application branches do not replace R under this supplied logic.
| Unavailable | Remaining expression | Service |
|---|---|---|
| A | R AND B | Works |
| B | R AND A | Works |
| R | False AND(A OR B) | Stops |
Remove one component at a time
- Retain AND and OR meanings
- Set failed component to false
- Evaluate the full expression
An unlisted alternative resolver cannot be assumed.
Which single failure stops both branches?
Show the worked answer
R. A or B alone can fail while the other branch remains usable, but both require R. The modeled single-component cut set is{R}.
Identify the common cut
| Case | Decision | Reason |
|---|---|---|
| A unavailable | Service remains | R andB remain |
| R unavailable | Service stops | Shared prerequisite absent |
Preserve the graph when discussing another branch. A third branch that also requires R would not fix this modeled cut.