HOMEWORK PROBLEM 2_7         INTRODUCTION TO Ada II   586.2

PURPOSE:      To learn more about access types, balanced binary trees,
              and reading disk files.

END RESULT:   A complete Ada program that is a main procedure
              that WITH's a package containing the binary tree
              manipulation routines INSERT,FIND,DELETE from HW2_6.

PROBLEM:      Write an Ada main procedure to read
              PUSERS:[ADA.ADACLASS]HW2_7.DAT . This file can be
              read by TEXT_IO using OPEN and GET_LINE. The name
              comes first with one blank, then the phone number.
              Put the information in your binary tree. Then run 
              the program interactively, giving a name and getting a
              phone number back. With an auto dialer, you could
              type in a name and automatically phone the person
              or computer.

TURN IN:      Printout of compilation of main procedure and
              package ( with no errors!)
              Printout of execution for some built in test data.

OBSERVE:      These tree manipulation routines are messy if recursive
              procedures and functions are not used. These happen
              to be in the class of "simple" recursive routines that
              can be thoroughly tested to be sure they terminate.

READING :     MIL-STD-1815A 3.8 plus use the index for all
                                references to "access"
              Barnes   11.3

EXTRA :       For extra credit make the INSERT and DELETE work
              to maintain a balanced binary tree. This uses the
              balance factor  BF. The INSERT is not too difficult
              but the DELETE is a bear! It turns out that just plain
              binary trees are very inefficient. But, balanced binary
              trees are very efficient. If the tree is maintained
              in balanced form at most  log2 N searches are needed
              for an INSERT, FIND or DELETE. On a Baltimore phone
              book N is a large number! An unbalanced tree could be
              the worse possible structure if the names were entered
              alphabetically. Zzepth could be all day checking his
              phone number. FORTRAN routines ( for samples ) are on
              PUSERS:[ADA.ADACLASS]BTINSR.FOR  BTDEL.FOR

 NOTE:        The files TACCESS*.ADA on ECLUS::PUSERS:[ADA.ADACLASS] are
              a sequence of approaches for various styles of use of
              access types with tree structures.