The first step of the Pre-Apply phase is to validate the content of the Change Set to see if the Change Set is eligible to be applied. As the Apply operation involves both database read and write operations, the user performing the operation must have the appropriate read and write permissions for each Business Object defined in the Change Set. If the user does not have the appropriate permissions, then the Apply process is terminated.
Next, the infrastructure creates a revert Change Set for undo purposes. It does so by capturing the current state of the database with respect to each of the Business Objects in the Change Set. That is, for each Business Object defined in the Change Set, the infrastructure will identify if the Business Object already exists in the target database. Since the business logic for determining the existence of a Business Object is very specific to the Business Object type, the infrastructure delegates the call to the ExistenceBOM in order to get the desired results.
As part of this phase, BOMs are used as follows: