A STRUCTURE field description  statement  defines  a  field  that  is
  divided into one or more subordinate fields.

1  –  Syntax Rules

   o  The field name you assign can be up to 31 characters from the set
      A-Z,  0-9,  _,  and $.  The first character must be a letter from
      A-Z, and the last character can not be _ or $.  You can use 8-bit
      alphabetic characters in field names.

   o  If you use an asterisk (*) instead of a field-name, you create an
      unnamed field.

   o  If you do not specify a data type for  the  STRUCTURE,  the  CDDL
      assigns it the UNSPECIFIED data type.

   o  Subordinate  field  description  statements  describe  contiguous
      portions of the field described by the STRUCTURE.

   o  There  must  be  at  least  one  subordinate  field   description
      statement.    A   subordinate  field  can  be  an  elementary,  a
      STRUCTURE, a COPY, or a VARIANTS field.

   o  CDDL accepts the keyword GROUP as a synonym  for  STRUCTURE,  but
      the compiler issues a warning when you use GROUP.

   o  You must terminate the STRUCTURE  and  the  END  statements  with
      periods.

2  –  Usage Notes

   o  Unnamed fields are similar to FILLER fields in  VAX  COBOL.   You
      can  use  them  to  format print records or to reserve space in a
      record for future additions.

   o  In a STRUCTURE field, you can use  any  field  attribute  clauses
      allowed in an elementary field.  However, if you use the DATATYPE
      field description statement, you cannot create subordinate fields
      that exceed the length of the structure field.

   o  A STRUCTURE field cannot contain the VIRTUAL FIELD datatype.

   o  Although the CDDL compiler accepts data type  specifications  for
      STRUCTURE  fields,  the  feature  can  not  be  supported  by the
      language or language processor you use with the CDD.   Make  sure
      the  definitions  you  store  in the dictionary are valid for the
      processor that will use them.

   o  All fields, except BIT fields, begin on the first byte  following
      the  preceding  field.   BIT  fields begin on the bit immediately
      following the preceding field.   You  can  modify  this  starting
      position with the ALIGNED clause.

3  –  Example

  You can nest STRUCTURE field description statements.   The  STRUCTURE
  field  ADDRESS,  for  example,  has  a  subordinate  STRUCTURE field,
  ZIP_CODE.

  ADDRESS STRUCTURE.
      STREET                    DATATYPE IS TEXT
                                SIZE IS 30 CHARACTERS.
      CITY                      DATATYPE IS TEXT
                                SIZE IS 30 CHARACTERS.
      STATE                     DATATYPE IS TEXT
                                SIZE IS 2 CHARACTERS.
      ZIP_CODE STRUCTURE.
          NEW                   DATATYPE IS UNSIGNED NUMERIC
                                SIZE IS 4 DIGITS
                                BLANK WHEN ZERO.
          OLD                   DATATYPE IS UNSIGNED NUMERIC
                                SIZE IS 5 DIGITS.
      END ZIP_CODE STRUCTURE.
  END ADDRESS STRUCTURE.