A relational valued value subclass in which values are stored as a single String object for the name of the object instance to which it is linked.
If the relational value is not linked to any object, then the String value is set to the empty String: "".
A string representing the object target of this value. Targets are specified by the object name identifier.
If the relational target is unset, then this value will be set to the empty string "", which is the default value.
Returns whether the value has been set to a meaningful value. Unset values
typically happen when a new object instance has been created by not had its
values set. Leaving values unset will result in exceptions being thrown
to prevent errors in underspecified states.
Removes a specific relational target from the relational value in relational attribute. If the relational
attribute does not have this target specified, then nothing happens. This method is primarily useful
for multi-target relational attributes, but if the attribute is a single-target relational attribute
and its one currently set target is the one passed to this method, then this method will clear the