RFC 819 (rfc819) - Page 2 of 18

Domain naming convention for Internet user applications

RFC 819                                                     August 1982;


   collection of arcs, where arcs are identified by ordered pairs of
   distinct nodes [1].  Each node of the graph represents a domain.  An
   ordered pair (B, A), an arc from B to A, indicates that B is a
   subdomain of domain A, and B is a simple name unique within A.  We
   will refer to B as a child of A, and A a parent of B.  The directed
   graph that best describes the naming hierarchy is called an
   "in-tree", which is a rooted tree with all arcs directed towards the
   root (Figure 1). The root of the tree represents the naming universe,
   ancestor of all domains.  Endpoints (or leaves) of the tree are the
   lowest-level domains.

                         U
                       / | \
                     /   |   \          U -- Naming Universe
                    ^    ^    ^         I -- Intermediate Domain
                    |    |    |         E -- Endpoint Domain
                    I    E    I
                  /   \       |
                 ^     ^      ^
                 |     |      |
                 E     E      I
                            / | \
                           ^  ^  ^
                           |  |  |
                           E  E  E

                                Figure 1
                 The In-Tree Model for Domain Hierarchy

   The simple name of a child in this model is necessarily unique within
   its parent domain.  Since the simple name of the child's parent is
   unique within the child's grandparent domain, the child can be
   uniquely named in its grandparent domain by the concatenation of its
   simple name followed by its parent's simple name.

      For example, if the simple name of a child is "C1" then no other
      child of the same parent may be named "C1".  Further, if the
      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


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