The Migrate system
Foundationally, the Migrate system is a backend API framework built around ETL concepts. Given the need to support diverse source and destination requirements, it must be highly configurable to work properly. This framework has been used to allow developers to address all of the migration-specific needs with defined plugins, configurations, and so on.
Beyond the API, the Migrate system includes the state of the migrations specific to the Drupal application in which migrations are run. This state maintains useful information, such as which migrations are registered on the application, what content has been successfully or unsuccessfully migrated per migration, what content has not yet been migrated per migration, and execution logs of every migration execution. Given the Migrate system is specific to a Drupal application, developers are empowered to run migrations on their local systems or non-production environments before running a migration on production.
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