An undiscriminated schema is a schema type  that  has  not  been
  provided  actual  discriminants.  You can use an undiscriminated
  schema as the domain type of a pointer  or  as  the  type  of  a
  formal parameter.  For example:

  TYPE
     Ptr_to_Array_Template = ^Array_Template;
     Array_Template( Upper_Bound : INTEGER )

  The Array_Template schema is not a complete description of data.
  It  is  not  a  valid  data  type  until  you  provide an actual
  discriminant that designates the upper  boundary  of  the  array
  template.