In the above code listing for the Agent class, we can also see that there is a @Unique annotation on the getLoginName() getter method (in addition to the @AttributeProperty annotation). This special annotation (also from the org.picketlink.idm.model.annotation package) is used to indicate to PicketLink that a unique constraint must be enforced on the property value - i.e. no two Agent objects (or their subclasses) may return the same value for getLoginName().