The first statement in a Natural program written in
structured mode must always be a
DEFINE DATA
statement which is used to define fields for use in a program.
This document covers the following topics:
In the DEFINE
DATA statement, you define all the fields - database fields
as well as user-defined variables - that are to be used in the program.
There are two ways to define the fields:
The fields can be defined within the DEFINE DATA
statement itself (see below).
The fields can be defined outside the program in a
local or global data area, with
the DEFINE DATA statement referencing that data area (see
below).
If fields are used by multiple programs/routines, they should be defined in a data area outside the programs.
For a clear application structure, it is usually better to define fields in data areas outside the programs.
Data areas are created and maintained with the source editor.
In the first example
below, the fields are defined within the DEFINE DATA statement of
the program. In the second
example, the same fields are defined in a
local data area (LDA), and the
DEFINE DATA statement only contains a reference to that data
area.
The following example illustrates how fields can be defined within the
DEFINE DATA
statement itself:
DEFINE DATA LOCAL 1 VIEWEMP VIEW OF EMPLOYEES 2 NAME 2 FIRST-NAME 2 PERSONNEL-ID 1 #VARI-A (A20) 1 #VARI-B (N3.2) 1 #VARI-C (I4) END-DEFINE ...
The following example illustrates how fields can be defined in a local data area (LDA):
Program:
DEFINE DATA LOCAL USING LDA39 END-DEFINE ...
Local Data Area LDA39:
I T L Name F Leng Index/Init/EM/Name/Comment
- - - -------------------------------- - ---- ---------------------------------
V 1 VIEWEMP EMPLOYEES
2 NAME A 20
2 FIRST-NAME A 20
2 PERSONNEL-ID A 8
1 #VARI-A A 20
1 #VARI-B N 3.2
1 #VARI-C I 4
The following topics are covered:
Level numbers are used within the DEFINE DATA statement to
indicate the structure and grouping of the definitions. This is relevant
with:
Level numbers are 1- or 2-digit numbers in the range from 01 to 99 (the leading zero is optional).
Generally, variable definitions are on Level 1.
The level numbering in view definitions, redefinitions and groups must be sequential; no level numbers may be skipped.
If you define a view, the specification of the view name must be on Level 1, and the fields the view is comprised of must be on Level 2. (For details on view definitions, see Database Access.)
DEFINE DATA LOCAL 1 VIEWEMP VIEW OF EMPLOYEES 2 NAME 2 FIRST-NAME 2 BIRTH ... END-DEFINE
The definition of groups provides a convenient way of referencing a series of consecutive fields. If you define several fields under a common group name, you can reference the fields later in the program by specifying only the group name instead of the names of the individual fields.
The group name must be specified on Level 1, and the fields contained in the group must be one level lower.
For group names, the same naming conventions apply as for user-defined variables.
DEFINE DATA LOCAL 1 #FIELDA (N2.2) 1 #FIELDB (I4) 1 #GROUPA 2 #FIELDC (A20) 2 #FIELDD (A10) 2 #FIELDE (N3.2) 1 #FIELDF (A2) ... END-DEFINE
In this example, the fields #FIELDC, #FIELDD
and #FIELDE are defined under the common group name
#GROUPA. The other three fields are not part of the group. Note
that #GROUPA only serves as a group name and is not a field in its
own right (and therefore does not have a format/length definition).
If you redefine a field, the REDEFINE option must be
on the same level as the original field, and the fields resulting from the
redefinition must be one level lower. For details on redefinitions, see
Redefining
Fields.
DEFINE DATA LOCAL
1 VIEWEMP VIEW OF STAFFDDM
2 BIRTH
2 REDEFINE BIRTH
3 #YEAR-OF-BIRTH (N4)
3 #MONTH-OF-BIRTH (N2)
3 #DAY-OF-BIRTH (N2)
1 #FIELDA (A20)
1 REDEFINE #FIELDA
2 #SUBFIELD1 (N5)
2 #SUBFIELD2 (A10)
2 #SUBFIELD3 (N5)
...
END-DEFINE
In this example, the database field BIRTH is redefined as
three user-defined variables, and the user-defined variable
#FIELDA is redefined as three other user-defined variables.
The storage area, in which all user-defined variables are stored, always begins on a double-word boundary.
If a DEFINE DATA statement is used, all data blocks (for
example, LOCAL, GLOBAL blocks) are double-word
aligned, and all hierarchical structures (view definitions and
groups) on
Level 1 are full-word aligned. Redefinitions, scalar and array variables are
not aligned, even if they are defined at level 1.
Alignment within the data area is the responsibility of the user and is governed by the order in which variables are defined to Natural.