System

{{entity:Railway Signalling System}} decomposition, final first-pass session. All 11 subsystems previously decomposed across sessions 300–309. This session focused on completion assessment, orphan remediation, verification gap closure, and first-pass-complete gate. Status moved from in-progress to first-pass-complete. Baseline DECOMP-2026-03-19 created.

Decomposition

The system comprises 11 subsystems and 55 components with 66 PART_OF and 68 CONNECTS relationships forming a complete structural and interface graph. The {{entity:Computer-Based Interlocking}} ({{hex:50F57958}}) sits at the architectural centre with the highest interface count — receiving track occupancy from {{entity:Train Detection Subsystem}}, issuing signal commands to {{entity:Colour-Light Signalling Output}}, driving {{entity:Points and Crossing Drive System}}, triggering {{entity:Level Crossing Protection System}}, exchanging route status with {{entity:ETCS Radio Block Centre}}, accepting commands from {{entity:Signaller Workstation}} via {{entity:Traffic Management System}}, and reporting state to {{entity:Signalling Diagnostic and Monitoring System}}.

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

Analysis

Cross-domain similarity search on {{entity:Computer-Based Interlocking}} revealed 91% Jaccard similarity with {{entity:Naval Combat Management System}} ({{hex:51FD7959}}) — both are real-time safety-critical processing hubs that fuse multi-source sensor inputs, enforce deterministic response timing, and command distributed actuators. The shared trait pattern (powered, active, processes signals/logic, outputs effect, safety-relevant) confirms the CBI is correctly classified as the railway equivalent of a combat management processor: the central decision authority with the tightest timing and highest integrity requirements.

Lint produced 7 findings (0 high, 1 medium, 6 low). The medium finding flags “operating hour” lacking statistical parameters in {{stk:STK-NEEDS-OPS-001}} and {{sys:SYS-REQS-FUNC-004}} — a legitimate observation that should be addressed in QC by adding confidence intervals and test conditions to MTBF-related requirements. Five ontological ambiguity findings (abstract system vs physical component classifications) were reviewed and acknowledged as correct: the top-level system is an abstract engineered concept while its UPS, workstation, and controller components are physical objects.

Requirements

Resolved 4 orphaned subsystem requirements by creating trace links to parent system requirements: {{sub:SUB-REQS-FUNC-060}} (signal proving lamp reporting) derives from {{sys:SYS-REQS-FUNC-003}}; {{sub:SUB-REQS-FUNC-070}} (CMS aggregation) derives from {{sys:SYS-REQS-FUNC-003}}; {{sub:SUB-REQS-FUNC-071}} (remote diagnostic read-only isolation) derives from {{sys:SYS-REQS-FUNC-001}}; {{sub:SUB-REQS-FUNC-089}} (timetable CIF validation) derives from {{sys:SYS-REQS-FUNC-001}}. Created 4 verification entries ({{sub:VER-TEST-082}} through {{sub:VER-TEST-085}}) covering lamp degradation injection, CMS peak-load latency, adversarial remote diagnostic write testing, and timetable conflict injection. Added system-level end-to-end integration test {{sub:VER-TEST-086}} exercising the full detection-to-protection safety chain (Wheel Sensor through CBI to Signal Aspect Driver) with 500ms sub-budget for safety actions and 1000-cycle statistical validation.

Final metrics: 245 requirements (6 STK, 7 SYS, 90 SUB, 45 IFC, 11 ARC, 86 VER). Verification coverage 64% of SUB+IFC requirements. Remaining 11 orphans are all architecture decision records — expected and acceptable.

Next

System is now first-pass-complete and ready for QC review (Flow C). QC should address: the medium lint finding on “operating hour” statistical parameters, verify trace chain completeness across all 5 linkset types, check that degraded-mode requirements across all subsystems include quantified minimum performance thresholds, and close the remaining 36% VER gap on subsystem requirements. The CBI-to-Naval CMS cross-domain analog may suggest missing failure mode requirements that naval systems typically carry.