# Response Data Collection & Management

- [Schema (variables)](/response-data-collection-and-management/variable-schema.md): Use and classify answers and other data once it has been collected.
- [Variables from questions](/response-data-collection-and-management/variable-schema/variables-from-questions.md)
- [Externally provided variables](/response-data-collection-and-management/variable-schema/external-answers.md): Capture values passed into flows, even if not collected in questions (also known as hidden fields).
- [Calculated variables](/response-data-collection-and-management/variable-schema/calculated-answers.md): Create derived variables by writing functions optionally using other variables
- [API lookups](/response-data-collection-and-management/variable-schema/api-answers.md): Store answers from API calls.
- [System Library variables](/response-data-collection-and-management/variable-schema/system-library-answers.md): Built-in answers about the responder's context and state.
- [Orphaned variables](/response-data-collection-and-management/variable-schema/orphaned-answers.md): A home for all your unresolved variable dependencies.