Contract for ECF identity
ECF IDs are immutable once constructed, and unique within the containing
Namespace.
ID instances are created via the Namespace.createInstance(...) method. This
method is called by the IDFactory.createID(...) methods for the given
Namespace. So, for example, to create an ID instance with the name "slewis":
ID id = IDFactory.getDefault().createID(namespace, "slewis");