<GROUP> :: <ELEMENTARY ITEM>

‘A name can be made unique if it exists within a hierarchy of names, and the name can be identified by specifying one or more higher-level names in the hierarchy. The higher-level names are called qualifiers, and the process by which such names are made unique is called qualification.’ COBOL Language Reference

In COBOL syntax, this qualification is done by using one or more phrases with IN or OF followed by a qualifier.

It is only necessary to specify enough qualification to make the name unique.

Difficulties with IN or OF operators :

• Data items must always be qualified from the lower level item to the higher level group item. This is not consistent with more modern programming languages, where variables are qualified from the higher level data structure to the variable of interest. This can thus be considered a backwards practice by younger COBOL programmers.
• This can make name completion (ie. content assist) less efficient.

TypeCobol proposes an alternative method to fully qualify data items when they are used. A new operator will be added for qualification of an element in a group.

Instead of saying ‘A of B’ or ‘A in B’ we will use a new syntax based on ‘::’ operator ‘B::A’

01 GR1.
   02 GR11.
      05 ELT11   PIC X.
   02 GR12.
      05 ELT11   PIC X.
   02 GR13.
      05 ELT12   PIC X.
01 GR2.
   02 GR21.
      05 ELT11   PIC X.
   02 GR22.
      05 ELT21   PIC X.
01  GRX          PIC X(100).

(1)

MOVE ELT11                  TO GRX

IGYPS0037-S "ELT11" was not a uniquely defined name. The definition to be used could not be determined from the context. The reference to the name was discarded.

(2)

MOVE ELT11 OF GR11          TO GRX

(3)

MOVE ELT11 OF GR1           TO GRX

IGYPS0037-S "ELT11 OF GR1" was not a uniquely defined name. The definition to be used could not be determined from the context. The reference to the name was discarded.

(4)

MOVE ELT11 OF GR11 OF GR1   TO GRX

(5)

MOVE ELT11 OF GR2           TO GRX

(6)

MOVE ELT11 OF GR21          TO GRX

(7)

MOVE ELT21 OF GR22 OF GR2   TO GRX

(8)

MOVE ELT21 OF GR22          TO GRX

(9)

MOVE ELT21 OF GR2           TO GRX

(10)

MOVE ELT21                  TO GRX

(1): ELT11 is an elementary item of groups GR11, GR12 and GR21. Then indicate ELT11 doesn’t allow to distinguish which ELT11 is to be moved.

(2): With the detail GR11 we have identified ELT11 among all the descriptions.

(3): With the detail of the group GR1 we still have two possibilities : GR11 and GR12.

(4): In this form we specify all hierarchy details; it is not mandatory (as we see in (2)) but valid.

(5), (6): With indication of sub-group or group, our item ELT11 is uniquely defined.

(7), (8), (9), (10): As ELT21 is only declared once, we can use it with all the hierarchy, part of it, or only the elementary item.

The following sentence:

A :: B :: C

will be translated as:

C OF B OF A

01 GR1.
   02 GR11.
      05 ELT11   PIC X.
   02 GR12.
      05 ELT11   PIC X.
   02 GR13.
      05 ELT12   PIC X.

01 GR2.
   02 GR21.
      05 ELT11   PIC X.
   02 GR22.
      05 ELT21   PIC X.
01  GRX          PIC X(100).

MOVE GR1::GR11::ELT11   TO GRX
MOVE GR2::GR21::ELT11   TO GRX

In COBOL providing the complete hierarchical path is not mandatory: it is only needed to give minimal group names to avoid any ambiguity on elementary items. In TypeCobol however, as a rule of thumb, the complete path to the elementary item should always be provided. Even if some parts of the path could be made implicit, in the general case, being explicit improves code readability and sustainibility.

In Cobol language for a multi-dimensional table, all subscripts are specified after the elementary item. With TypeCobol and new :: operator, each subscript will be mentioned at the exact level of the occurrence. Objective is to improve understanding and readability by using subscript at the level of the occursed element or group.

Examples

01 A.
    02 B OCCURS 10.
      03 C.
        04 D1 PIC X(10).
        04 D2 PIC X(10) OCCURS 10.

01 AA.
    02 B OCCURS 10.
      03 C.
        04 D1 PIC X(10).
        04 D2 PIC X(10) OCCURS 10.

In Cobol to address a D2 item we could use one of the following syntax:

D2 OF A (x y)

D2 OF C OF A (x y)

D2 OF B OF A (x y)

D2 OF C OF B OF A (x y)

Suggested syntax in TypeCobol with :: operator

A :: B (x) :: C :: D2 (y)

In Cobol, declaration of elements or groups not used without a name is possible. For Cobol syntax there is no impact because if we want to qualify an element of a group it is not necessary to give the complete hierarchy. The Cobol syntax for multi dimensional table is also not impacted by this, i.e. :

01  GROUPE.
    05            OCCURS 5.
			10   		OCCURS 5.
				15 ELEMENT1 PIC X.

In Cobol syntax we have all subscripts at the end then we address with

	ELEMENT-1 (i j)

Or

	ELEMENT-1 OF GROUPE (i j)

This has an impact on TypeCobol new operator ‘::’ because we should use some subscript without any name :

GROUPE::(i)::(j)::ELEMENT1

It should be considered as a best practice to avoid these groups.