Bidirectional, Inverse and Managed Relationships 

A relationship between two persistent capable classes is called bidirectional or inverse if there are corresponding relationship fields in both classes, whereas in the relational model, there is only one foreign key that holds the data.

A relationship field is called managed if the consistency is maintained by the implementation. For example, changes made to one side of a bidirectional relationship are reflected on the other side.

The SAP JDO Implementation does not support managed relationships. You have to ensure that the relationship fields are consistent.

To prevent duplicate inserts or multiple updates in the database, one side of a bidirectional relationship is marked as non-updatable. You can do this by setting the update property in the relationship-field metadata element to false .

You must not set the updateproperty in the relationship-field metadata element to false in a unidirectional relationship.