The goal of The Global Root Zone is a single unified name
space for the Internet.  To be more explicit, the goal is to be sure
that every IP address reachable through the Internet backbone can
also be uniquely named.  

This is an asymptotic goal.  DNS is a general mechanism, and nowhere
is it written in stone that a single connected name space must exist. 
The nature of DNS is such that an organization that wishes to set up
a competing root zone can do so.  Moreover, local roots on private
networks are commonplace. 

On the other hand, the existence of a Global Root zone is of
fundamental importance.  Much of the economic power in the Internet is
a function of convenient universal connectivity, and a universal name
space is a necessary component of that convenience. 

The "single unified name space" goal has certain implications for the
Root zone.  It must be extremely reliable; it must be "trustworthy";
it must abide by widely accepted operational practices; and so on. 

The Global Root Zone has, in practice, many more unique
characteristics than just sitting at the top of the tree.  For
example:

  1) Stability must emanate from the Root.  Clearly, if the Root is
  unstable, then no subdomain can be stable, and thus the requirements
  for stability are much greater on the Root Zone than on other zones. 

  This requirement of stability is not a surface requirement,
  although the rush to commercialize the Internet tends to mask its
  depth.  The Internet is on the cusp of being an indispensable part
  of the infrastructure of the civilized world, used by governments 
  in the prosecution of war and peace; used by hospitals; used by 
  power and water companies to manage their systems.  In time we can 
  expect traffic lights to be controlled through the internet.

  2) The Root zone contains the top of the special .arpa zone, and
  thus is entwined in the technical functioning of lower level
  protocols in the Internet. 

  3) Currently the majority of the domains in the Root zone have
  political significance (the ccTLDs). 

  4) IANA has essentially no discretionary authority to remove any of
  the current TLDs.  The ccTLDs are controlled by ISO and political
  concerns; .com, .org, and .net cannot be removed for practical
  reasons; .gov and .mil cannot be removed for political reasons;
  .edu can't be removed for historical reasons; .int can't be removed
  for political reasons; and the .arpa domain cannot be removed for
  practical and technical reasons.  That is, the Root Zone has a
  historical fiduciary character. 


These characteristics and more create an expectation concerning the
nature of the root zone.  There is an implied social contract with
all the users of the Internet:
     
  A Root zone operator that takes its task seriously, and likewise
  wishes to be taken seriously, must assume a responsibility to those
  end users, even though the end users have no direct contact with the
  Root zone operator. 

  That is, the Root Zone Operator cannot disenfranchise
  end-users of the DNS: the Root Zone Operator will not willfully
  cause users to lose connectivity to the global name space.