Explain the term 'data schema' and its importance.

Official answer

A data schema describes structural rules: entities or record fields, types, keys, relationships and constraints. A useful contract also documents meaning, units, nullability and the grain of a record. In some databases, schema additionally names a namespace containing objects; distinguish that usage from the data model.

For an order, define whether amount is an integer minor-unit quantity or a decimal, record its currency, and distinguish placed_at from ingested_at. A field named timestamp without those semantics is an incomplete contract even if its type is valid.

Schemas help producers and consumers agree on interpretation and let systems reject incompatible records. Constraints enforce only what they express: a positive amount can still be wrong, and a foreign key does not establish that the requester is authorized to see the referenced row.

Version schemas and test changes against active readers/writers and historical data. A rename or change of units can break consumers despite an unchanged primitive type. Indexes and access controls are related design choices with their own tradeoffs; a schema alone does not guarantee speed, confidentiality or a lossless migration. Validate those properties separately.