# Relationship history for MSHA mine 0405148

Current hierarchy: **Dana K  Ferrell; Steve  Norberg → Sd Engineering Inc → S.D. PORTABLE PLANT #2**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-13T11:19:05.459773+00:00

## Valid-time edges

- **controller_controls_mine:** Steve  Norberg et al → S.D. PORTABLE PLANT #2; 1986-12-01 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Sd Engineering Inc → S.D. PORTABLE PLANT #2; 1991-06-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Steve  Norberg et al → Sd Engineering Inc; 1991-06-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Dana K  Ferrell et al → Sd Engineering Inc; 1991-06-01 to current/open; source msha-controller-operator-history