Say, that you want to store the details about the Employees working in the Company. Each EMPLOYEE-RECORD detail is generally 56 characters. To store Employee data in the COBOL Program, I create an EMPLOYEE-RECORD Storage Area as follows.
I know that, EMPLOYEE-RECORD data contains the Name of the Employee(30 chars) and the address of the employee(26 chars). I break down EMPLOYEE-RECORD into NAME and EMP-ADDRESS Fields as follows.
But, the name itself consists of First-name(10), Middle-name(10) and Last-name(10). Employee-Address Data consists of Street(10), City(10) and Pin-code(06). I can provide an extra-level of detailed breakup.
This way, you can take a 01-Level Data-item, and break it down further into smaller storage-areas, depending on the granularity-of-detail, you wish to capture.
77-level storage-areas are independent data-items, they cannot be broken down further into smaller storage areas. Moreover, they cannot participate under a bigger storage area.
If EMPLOYEE-RECORD were to be an 77-Level Independent Variable, it would look like this. Note that, now you can’t chop it!