PropertySet is a persistence-agnostic module that can be used to fulfill storage requirements in applications that can change constantly. An example of this might be a "User Preferences" storage device. It may be impossible to know what the user can store at any given time in your application's lifecycle, so employing a PropertySet can help. Backed by XML, EJB, Ofbiz, JDBC, Castor JDO, or any other persistence mechanism, you can provide a complete typed key-value pair implementation.