Explain source-to-target mapping.

Source-to-target mapping is a core concept in ETL (Extract, Transform, Load) processes where data from a source system is transformed and loaded into a target system. The mapping defines how each source field corresponds to a target field, including data type conversions, transformations, and business rules. A typical mapping document contains:

1. Source field – name, data type, and source system.
2. Target field – name, data type, and target system.
3. Transformation logic – arithmetic, concatenation, lookup, or custom functions.
4. Business rules – conditions, defaults, or validations.
5. Cardinality – one-to-one, one-to-many, or many-to-one relationships.
6. Metadata – comments, version, and owner.

Mapping can be manual or generated by tools like Informatica, Talend, or custom scripts. It ensures data consistency, quality, and traceability. During development, mapping is validated by unit tests and data profiling. In production, mapping changes are versioned and deployed through CI/CD pipelines to avoid data drift. Proper source-to-target mapping reduces ETL errors, improves maintainability, and provides a clear audit trail for compliance and troubleshooting.