ORIGINAL COMPANY-CONTEXT PRACTICE
Trace wafer-lot lineage through splits and merges
Original practice scenario: Design a hypothetical manufacturing lineage service where a lot can split, merge or undergo rework. How would you answer which finished units share an upstream process step?
Written for independent practice using company context; this is not a verified question from a company interview.
A REASONED APPROACH
Model answer.
Represent genealogy as immutable transformations between identified material units or lots. A single parent column cannot capture both splits and merges without losing provenance.
Work through it
- Store each transformation with input identities, output identities, quantities, process-step version and event time; validate conservation rules appropriate to the process.
- Build traversable upstream and downstream edges with indexes by material and transformation, retaining corrections as new versions rather than overwriting history.
- Support bounded lineage queries and test partial splits, repeated rework and missing upstream events, returning incomplete evidence explicitly.
Tradeoffs to discuss
- Fine-grained unit lineage improves precision but creates more records; lot-level lineage is cheaper while increasing the scope of affected material.
Common pitfalls
- Prevent accidental cycles or distinguish a new rework generation from an impossible self-reference.
- A complete graph does not establish that every source scan was recorded correctly; retain reconciliation and source-quality controls.