3.0 KiB
3.0 KiB
Quality Criteria: System Sequence Diagram (SSD)
Metadata
| Key | Value |
|---|---|
| ID | QC-SSD-001 |
| CrossReference | QC-UC-001, QC-DM-001, QC-OC-001 |
| DomainLanguages | IT Professional English |
Version History
| Date | Status | Author | Reviewer | Change | Commit |
|---|---|---|---|---|---|
| 2026-10-01 | Accepted | Jens Tirsvad Nielsen | S07 | First public release (1.0.0) | — |
Purpose
The System Sequence Diagram illustrates the interaction between an actor and the system as a black box, for one use case scenario. Its quality ensures that the boundary between external actors and internal system behavior is captured accurately before internal design begins.
Quality Criteria Checklist
Level: Mandatory criteria are the baseline every instance must meet; Optional criteria are advanced and may be deferred.
| # | Criterion | Level | ISO/IEC 25010 Characteristic(s) | Notes |
|---|---|---|---|---|
| 1 | Input/output messages match the corresponding Use Case's main success scenario step-for-step | Mandatory | Functional Suitability | The primary purpose of an SSD; deviations must be justified |
| 2 | Actor and System are treated strictly as black boxes (system shown as :System) |
Mandatory | Maintainability, Compatibility | No internal object interactions may appear on an SSD |
| 3 | Object creation/destruction of the System instance handled explicitly where relevant | Optional | Functional Suitability | Applies mainly to session/transaction-scoped interactions |
| 4 | Return values are shown for operations that produce one, using dashed return arrows | Mandatory | Functional Suitability | Missing return arrows hide important system responses |
| 5 | Alternate/exceptional flows are represented separately (or explicitly out of scope noted) | Mandatory | Reliability | Prevents conflating happy-path and error-path in a single diagram |
| 6 | Message names are verb phrases consistent with the use case's system responsibilities | Optional | Usability, Maintainability | Improves traceability to Operation Contracts |
| 7 | Diagram references the specific Use Case (name and ID) it depicts | Mandatory | Maintainability | Required for backward traceability |
Common Defects
- Showing internal objects or classes instead of a single
:Systemlifeline - Message sequence not matching the use case's main success scenario
- Missing return values for queries or commands that report a result
- Mixing multiple use case scenarios into a single SSD without separation
- No reference to the source Use Case
Traceability Rule
- Backward: Must trace to a specific Use Case checklist (QC-UC-001) main success scenario and the Domain Model checklist (QC-DM-001) concepts used as message parameters/return types
- Forward: Feeds into the Operation Contract checklist (QC-OC-001), one per system operation (message) shown on the SSD