We plan a full redesign of the `update()`/`commit()` functionality of AAS objects for synchronization with an external data source. * Instead of overriding these functions for different data sources, all `Referable` objects will include a `source` attribute with an URI representation of their data source. The URI's schema is used to determine the correct backend/client. * `update()` and `commit()` should always effect the object itself and all (recursively) included objects * If the object itself has no data source/backend itself, the next higher object with a data source is used to update the object's data. * After the update, all included objects that are linked with an own data source are updated recursively in a top-down manner. * An object is always committed to its own data source and the data sources of all its ancestors in the object hierarchy. * The included objects are committed recursively. (TODO: Define order of committing.)