System

{{entity:Railway Signalling System}} {{hex:50F77A59}}, interim QC review. The decomposition is in-progress with 4 subsystems fully decomposed ({{entity:Computer-Based Interlocking}}, {{entity:Train Detection Subsystem}}, {{entity:ETCS Radio Block Centre}}, {{entity:Level Crossing Protection System}}). Project statistics at session start: 97 requirements, 71 trace links, 10 diagrams (4 pairs of duplicates), 9 orphan requirements. Last QC was session 299; this interim QC covers work from sessions 300–302.

Findings

Duplicate diagrams (4 pairs). Each decomposed subsystem had an empty stub diagram alongside its populated internal diagram. Context diagram similarly duplicated. The empty stubs had zero connectors — likely artefacts of diagram creation where the first attempt failed and was immediately re-created.

Orphan requirements: 9 total, 4 actionable. Five ARC decision records are expected to be unlinked. The four actionable orphans: {{stk:STK-NEEDS-OPS-004}} (maintainability, no SYS derivation), {{sys:SYS-REQS-ENV-007}} (environmental, no STK parent), {{sub:SUB-REQS-FUNC-009}} (EMT access control, no SYS parent), {{sub:SUB-REQS-FUNC-028}} (juridical recording, no SYS parent).

Verification coverage gap. Only 8/35 SUB requirements had VER links (23%). IFC coverage was 100% (18/18). Combined SUB+IFC coverage was 26/53 (49%), just below the 50% threshold.

Spray patterns: 3 SYS reqs with 5+ SUB links. {{sys:SYS-REQS-FUNC-005}} (ETCS MA computation) has 8 SUB links spanning the entire RBC-Euroradio-GSM-R-gateway chain — each with specific latency-budget rationale. {{sys:SYS-REQS-FUNC-003}} (redundancy) has 7 SUB links cascading the no-single-failure requirement to every SIL 4 subsystem. {{sys:SYS-REQS-FUNC-001}} (interlocking logic) has 6 links. All links have genuine derivation rationale; none are mechanical.

Lint findings: 4 (2 medium, 2 low). Two medium findings about abstract metrics (“operating hour”, “vpu”) lacking statistical context in requirements — acknowledged but not critical for interim QC. Two low findings about ontological ambiguity (system-level abstract vs physical component classification, expected by design) and 31 VER/ARC entries without “shall” keyword (correct for verification procedures and architecture decisions).

Rationale and verification fields: 0 missing. All 97 requirements had both rationale and verification populated. All 71 trace links had rationale.

Corrections

Deleted 4 duplicate diagrams: empty stubs for Context (diagram-1773853405100), CBI Internal (diagram-1773857017407), Train Detection Internal (diagram-1773860594238), and ETCS RBC Internal (diagram-1773864249440). Retained the populated diagrams in each case.

Linked 4 orphan requirements: {{stk:STK-NEEDS-OPS-004}} → {{sys:SYS-REQS-FUNC-003}} (maintainability drives redundancy for rapid repair). {{stk:STK-NEEDS-PERF-003}} → {{sys:SYS-REQS-ENV-007}} (availability drives environmental specification). {{sys:SYS-REQS-FUNC-001}} → {{sub:SUB-REQS-FUNC-009}} (interlocking safety drives EMT access control). {{sys:SYS-REQS-FUNC-005}} → {{sub:SUB-REQS-FUNC-028}} (ETCS MA requirement drives juridical recording).

Created 6 verification entries: {{sub:VER-027}} for route-locking (SUB-REQS-FUNC-002), {{sub:VER-028}} for Object Controller command authentication (SUB-REQS-FUNC-005), {{sub:VER-029}} for VPU data integrity (SUB-REQS-FUNC-006), {{sub:VER-030}} for 2oo3-to-2oo2 degraded mode (SUB-REQS-FUNC-008), {{sub:VER-031}} for axle counter accuracy (SUB-REQS-FUNC-015), {{sub:VER-032}} for axle count discrepancy fail-safe (SUB-REQS-FUNC-016). Combined SUB+IFC VER coverage now 31/53 (58%).

flowchart TB
  n0["Railway Signalling System"]
  n1["Computer-Based Interlocking"]
  n2["Train Detection Subsystem"]
  n3["ETCS Radio Block Centre"]
  n4["Colour-Light Signalling Output"]
  n5["Points and Crossing Drive System"]
  n6["Level Crossing Protection System"]
  n7["Traffic Management System"]
  n8["Signaller Workstation"]
  n9["Signalling Communication Network"]
  n10["Signalling Power Supply System"]
  n11["Signalling Diagnostic and Monitoring System"]
  n2 -->|Track occupancy data| n1
  n1 -->|Signal aspect commands| n4
  n1 -->|Point drive commands| n5
  n5 -->|Point detection feedback| n1
  n1 -->|Crossing activation trigger| n6
  n1 -->|Route status for MA computation| n3
  n7 -->|Automatic route requests| n1
  n1 -->|Interlocking state display| n8
  n8 -->|Signaller commands| n1
  n9 -->|Data transport| n1

Residual

22 SUB requirements still lack VER links. The remaining un-verified requirements are concentrated in the RBC subsystem (SUB-REQS-FUNC-021 through 029, excluding 028) and Level Crossing subsystem (SUB-REQS-FUNC-031 through 035, excluding 034). These should be addressed in the next decomposition session or a dedicated VER session. The duplicate ARC entries (ARC-SYS-ARC-002 and ARC-SYS-ARC-003 both referencing Train Detection Subsystem) should be investigated — one may be a duplicate.

Next

Continue Railway Signalling System decomposition. Priority targets: Signalling Communication Network, Signalling Power Supply System, and Signalling Diagnostic and Monitoring System — these three subsystems have no internal decomposition or SUB requirements yet. The next session should also extend VER coverage for RBC and Level Crossing SUB requirements.