Number 05/Failure & fragility/Engineering
The Interface Fraction
The quantity
The fraction of system failures occurring at boundaries between components rather than inside components.
01Why it matters
If interfaces dominate, design effort and testing effort are misallocated almost everywhere, because components are specified and tested far more rigorously than the links between them.
02Expected value
Above one half, and higher in systems assembled from independently developed parts.
03How it would be measured
Classify failure reports by location. Most maintenance databases already record it.
04What would refute it
A fraction near the component share of volume would remove the claim.