What does the term "schema on read" refer to?

The term "schema on read" refers to the practice of applying a schema to data at the time it is accessed or queried, rather than when it is stored. This approach allows for more flexibility, as the data can be ingested in its raw form without needing to conform to a predefined structure upfront. When a user or application queries the data, the relevant structure can be applied dynamically based on the specific needs of that query or the context in which the data is being used.

This contrasts with other approaches, such as "schema on write," where the data must fit a predefined structure before it is stored. By allowing the schema to be defined at the time of reading the data, users can adapt to changing data requirements and work with a wider variety of data types without being constrained by a rigid schema. This flexibility is particularly beneficial in data lakes and unstructured data environments.