# System Sequence Diagram: Study Flash Cards

## Metadata
| Key | Value |
| --- | --- |
| ID | SSD-001 |
| CrossReference | [UC-001], [DM-001], [OC-001] |
| Language | en |
| Domain | it |

## Version History
| Date | Status | Author | Reviewer | Change | Commit |
| --- | --- | --- | --- | --- | --- |
| 2026-10-14 | Deprecated | Jens Tirsvad Nielsen | AI as stand-in for S01 | Initial version | [c3fbcbc] |
| 2026-10-14 | Accepted | Jens Tirsvad Nielsen | AI as stand-in for S01 | Added chooseLevel; startStudySession returns the levels | pending |

---

## Source Use Case

Study Flash Cards ([UC-001]) — scenario: main success scenario, with the unknown button as one repetition.

## Diagram

```plantuml
@startuml
actor Learner as L
participant ":System" as S
L -> S : startStudySession()
S --> L : levels (100 words, 1000 words, all words)
L -> S : chooseLevel(level)
S --> L : card (word, language name)
... 3000 ms pass, the system turns the card over ...
S --> L : card (translation, language name)
L -> S : markKnown()
S --> L : next card (word, language name)
L -> S : markUnknown()
S --> L : next card (word, language name)
@enduml
```

## System Operations

| Step | Message | Parameters | Return | Use case step |
| --- | --- | --- | --- | --- |
| 1 | startStudySession | none | the levels to choose from | 1, 2 |
| 2 | chooseLevel | level | card to show, or "nothing left to learn" | 3, 4, 5 |
| 3 | (timer) turn the card over | none | the same card, translation side | 6 |
| 4 | markKnown | none | next card, or "nothing left to learn" | 7, 8, 9 |
| 5 | markUnknown | none | next card, or "nothing left to learn" | 7a, 9 |

The turn-over in step 3 is started by the system's own timer, not by a message from the Learner; it is shown as a return without a call, which is the one deviation from "every return answers a message". When the level is given at start (extension 3a of [UC-001]) the Learner's first message is `chooseLevel` and `startStudySession` is not sent.

## Alternate Flows

The extensions 3a, 4a, 5a, 7b and 9a of [UC-001] add no system operation of their own (they are errors, speech, timer and level handling inside the operations above); their behaviour is in [OC-001] as exceptions. They are out of scope of this diagram, which shows the main success scenario with `markUnknown` as the one alternate answer.

## Lifecycle Notes

The system instance lives for one run of the program. The words to learn are created when the level is chosen and saved after each `markKnown`.

---

[UC-001]: ./uc.md
[DM-001]: ../domain-model.md
[OC-001]: ./oc.md
[c3fbcbc]: https://git.tirsystem.com/Tirsvad-Udemy-100-days-of-code/031-flash-card/commit/c3fbcbcfaf799e0ae34aed7e14d3bc8a62f03db3