parent of this child is named "P1", then "P1" is a unique simple
      name in the child's grandparent domain.  Thus, the concatenation
      C1.P1 is unique in C1's grandparent domain.

   Similarly, each element of the hierarchy is uniquely named in the
   universe by its complete name, the concatenation of its simple name
   and those for the domains along the trail leading to the naming
   universe.

   The hierarchical structure of the Internet naming convention supports
   decentralization of naming authority and distribution of name service
   capability.  We assume a naming authority and a name server



 


RFC 819                                                     August 1982;


   associated with each domain.  In Sections 5 and 6 respectively the
   name service and the naming authority are discussed.

   Within an endpoint domain, unique names are assigned to 
   representing user mailboxes.  User mailboxes may be viewed as
   children of their respective domains.

   In reality, anomalies may exist violating the in-tree model of naming
   hierarchy.  Overlapping domains imply multiple parentage, i.e., an
   entity of the naming hierarchy being a child of more than one domain.
   It is conceivable that ISI can be a member of the ARPA domain as well
   as a member of the USC domain (Figure 2).  Such a relation
   constitutes an anomaly to the rule of one-connectivity between any
   two points of a tree.  The common child and the sub-tree below it
   become descendants of both parent domains.

                                 U
                               / | \
                             /   .   \
                           .     .   ARPA
                         .       .     | \
                                USC    |   \
                                   \   |     .
                                     \ |       .
                                      ISI

                                Figure 2
                      Anomaly in the In-Tree Model

   Some issues resulting from multiple parentage are addressed in
   Appendix B.  The general implications of multiple parentage are a
   subject for further investigation.

3.  Advantage of Absolute Naming

   Absolute naming implies that the (complete) names are assigned with
   respect to a universal reference point.  The advantage of absolute
   naming is that a name thus assigned can be universally interpreted
   with respect to the universal reference point.  The Internet naming
   convention provides absolute naming with the naming universe as its
   universal reference point.

   For relative naming, an entity is named depending upon the position
   of the naming entity relative to that of the named entity.  A set of
   hosts running the "unix" operating system exchange mail using a
   method called "uucp".  The naming convention employed by uucp is an
   example of relative naming.  The mail recipient is typically named by
   a source route identifying a chain of locally known hosts linking the




 


RFC 819                                                     August 1982;


   sender's host to the recipient's.  A destination name can be, for
   example,

      "alpha!beta!gamma!john",

   where "alpha" is presumably known to the originating host, "beta" is
   known to "alpha", and so on.

   The uucp mail system has demonstrated many of the problems inherent
   to relative naming.  When the host names are only locally
   interpretable, routing optimization becomes impossible.  A reply
   message may have to traverse the reverse route to the original sender
   in order to be forwarded to other parties.

   Furthermore, if a message is forwarded by one of the original
   recipients or passed on as the text of another message, the frame of
   reference of the relative source route can be completely lost.  Such
   relative naming schemes have severe problems for many of the uses
   that we depend upon in the ARPA Internet community.

4.  Interoperability