A Subordinate Reference entity provides a reference to a
 Naming Context entity that is beneath a Naming Context entity
 held by this DSA. The subordinate Naming Context entity might
 also be held by this DSA; it is not necessarily on a remote DSA.

 A subordinate reference enables a DSA to redirect requests for
 information that it does not hold. It also marks the point
 at which one naming context ends, and another begins.