A constraint relationship is a mechanism to ensure data integrity between a dependent file and a parent file. You need to pay attention to the constraint relationship when copying files.
A constraint relationship exists between a dependent file and a parent file when every non-null foreign key value in the foreign key access path of the dependent file matches a parent key value in the parent key access path of the parent file. A physical data file can be a parent or dependent file. However, a source physical file cannot be a parent or a dependent file.