Definition
What it would take to replace a system with an alternative that meets the same obligation. It is counted in staff-weeks of work, retained expertise, contractual exit terms, and the time before the alternative carries production load. Measured, it is a number; assumed, it is a guess.
It matters because substitution cost is the hinge between a working switch and institutional reversibility, and it is the factor that dominates exposure score in mature deployments. A high and unmeasured cost is how a right of exit becomes nominal.
MeasurableStructural
Tests that show it is in place
- The estimate is derived from a costed alternative, not from a vendor comparison sheet.
- Contractual exit terms and data egress costs are included in the figure.
- The estimate is validated at least once against a partial substitution actually performed.
Evidence to keep
- Artifact: A costed substitution study for the deployment, dated and owned.
- Behavior: A partial substitution performed in a rehearsal, with actuals compared to estimate.
- Metric: Staff-weeks and elapsed days to bring an alternative to production load.
- Metric unit: staff-weeks and elapsed days
- Data source: Substitution study, contract terms, and rehearsal actuals.
References