LEVEL NUMBER

• In COBOL, the hierarchy of variables can be specified using the level number concept.
• For example: - variables ‘DD’, ‘MM’ and ‘YYYY’ are three individual elementary data items. These three elementary items can be clubbed together to form a group data item named DATE. The organization for these variables is shown in below figure:-
  
• It is important to note that the memory space referred to by DATE variable is the combined memory space of DD, MM and YYYY variables.
• Benefit of such grouping is that programmer can now refer to the individual elementary data items ‘DD’, ‘MM’, ‘YYYY’ or directly to the group data item ‘DATE’.
• Below is declaration of variables for the above explained example:-
  01 DATE. (no PIC clause as it is group data item) 05 DD PIC X(2). 05 MM PIC X(2). 05 YYYY PIC X(4).

• Level number can range from 01 to 49. However there are some special purpose level numbers also exists such as 66, 77 and 88.
• Data items defined with level number can be of two types:-
  • Group Data Item:-
    • Data item that is further sub-divided are called as Group Data item.
    • Group data item do not have PICTURE clause
    • Group data item should be unique in a program
    • Group data items can have level number from 01 to 48
    • For example:- data item ‘DATE’ is Group data item which is further sub-divided into three data items ‘DD’, ‘MM’ and ‘YYYY’
  • Elementary Data Item: -
    • Data items that is not further sub-divided. For example:- data items ‘DD’, ‘MM’, ‘YYYY’ in above example are elementary data item as they are not further divided
    • Elementary data item must include a PICTURE clause
    • Elementary data item need not to be unique within same group as these data items can be uniquely referenced using OF keyword followed by group data item
    • Elementary data items can be declared at level number 77, 01 - 49
• Level 01 entries must begin in Margin A and can be continued to Margin B of coding sheet
• The other level entries i.e. 02-49, 66 and 88 can begin with Margin A and Margin B(i.e. column position 8 to 72)

Level Number	Description
01	Used to declare Group data item or Elementary data item. Data items is also referred to as Record when declared at this level
02-49	Used to declare Group data item or Elementary data item.
66	Used to declare data item with RENAMES clause
77	Used to declare independent data items. Data item declared at 77 level cannot be further sub-divided
88	Used to declare CONDITION NAME entry