SYSML21 — Supplement to SYSML21-685/686: nine SI.sysml unit declarations bind a value whose dimension is not the declared unit type's

Scope

This report adds evidence to SYSML21-685 and SYSML21-686 (both open, reported 21 Sep 2026 against SysML 2.0). It does not report a new defect. Please link or merge it with them.

1. Independent confirmation

We derived the same SI.sysml lines independently, by reducing each unit expression to its dimension and comparing it with the quantityDimension of the declared unit type: lines 137, 149, 163, 233, 239, 247, 286, 299 and 303. All nine are covered by SYSML21-685 (items 1 to 3) and SYSML21-686. Our root causes agree with theirs:

• ISQAtomicNuclear.sysml line 2527 declares doseEquivalentRate as DoseEquivalentValue, while its own documentation gives dimension L²·T⁻³. DoseEquivalentUnit (line 2520) is L²·T⁻². No rate value or unit type exists.
• MagneticDipoleMomentUnit is declared in both ISQAtomicNuclear.sysml (line 286, L²·I) and ISQElectromagnetism.sysml (line 1256, L³·M·T⁻²·I⁻¹). ISQ re-exports both.

2. Versions

• Present at SysML-v2-Release tags 2026-07 and 2026-09 (commit b7a6b770 for tag 2026-09).
• SI.sysml is unchanged at master (commit 9546486f), checked 2026-11-03.
• SYSML21-685 cites commit fb97b754 for 2026-09. The lines are the same.

3. Tool measurement and its limits

OpenSysML sysml-grpc v0.10.1, reading the published SI.sysml as a document, reports exactly lines 137, 149, 163, 233, 239, 247, 286 and 299, and nothing else in the file. In our measurement the pilot implementation does not check dimensions and is silent. Two observations complement item 4 of SYSML21-685:

• A value-versus-type dimension check cannot see line 136 (HartreeEnergyUnit), where the expression and the declared type agree and both are wrong. It is found only by comparing with the source quantity, as SYSML21-685 does.
• Line 303 is not reported. This is consistent with the tool resolving the name MagneticDipoleMomentUnit to the electromagnetic definition, which is right at 303 and wrong at 233 (our inference).

4. Reproducer

package Check {
    private import SI::*;
    private import ISQ::*;
    attribute u1 : TotalMassStoppingPowerUnit = eV*m^-2/kg;   // T^-2, expected L^4*T^-2
    attribute u2 : DoseEquivalentUnit = Sv/s;                  // L^2*T^-3, expected L^2*T^-2
}

5. Resolution detail

For SYSML21-685 item 3: add DoseEquivalentRateValue and DoseEquivalentRateUnit (L²·T⁻³) to ISQAtomicNuclear, retype doseEquivalentRate by them, and type lines 239, 286 and 299 by the new unit. For SYSML21-686: qualified names at lines 233 and 303, as proposed there.

6. Relevant KerML clauses

KerML 1.0 (formal/26-03-01), printed page numbers: Feature Values 7.4.11 (p. 66); FeatureValue 8.3.4.10.2 (p. 225); Feature Values Semantics 8.4.4.11 (p. 274). Name resolution: 8.2.3.5 (pp. 82 to 85). Open issues KERML11-30 and KERML11-145 concern Feature Values semantics and the checkFeatureValuationSpecialization constraint.