In systems migration and integration, what is the best definition of “legacy data” when introducing a new information system?

Introduction / Context:
Legacy data arises when organizations replace older applications. Properly understanding and handling legacy data is crucial for successful migration, continuity, and compliance (audit, retention, privacy).

Given Data / Assumptions:

• An older system contains business-critical records before the new system goes live.
• Migration or integration must preserve integrity, history, and meaning.
• Data quality issues are common in legacy sources.

Concept / Approach:
Legacy data is the information generated and stored by the predecessor system. Migration requires profiling, cleansing, transformation, and mapping to the new data model, often with master data reconciliation and historical retention strategies.

Step-by-Step Solution:

Verification / Alternative check:
Migration runbooks typically label source datasets from retired applications as “legacy” and plan ETL accordingly.

Why Other Options Are Wrong:
Newly-installed system data is not legacy.
Rejected data is a migration outcome, not a definition.
File system says nothing about being pre-upgrade.

Common Pitfalls:
Underestimating mapping complexity; assuming legacy codes align one-to-one with the new model; neglecting archival and legal retention needs.

Final Answer:
Data contained by a system used prior to the installation of a new system