Imagine you’re an archaeologist, but instead of digging up dinosaur bones, you’re unearthing a codebase written in COBOL. It might seem like deciphering ancient hieroglyphs at first, but fear not! This chapter is your Rosetta Stone. We’ll break down COBOL, not as a relic of the past, but as a language still powering critical systems today. Think of it as learning enough Latin to understand the roots of modern Romance languages – it gives you a powerful foundation.
This chapter provides a concise and practical guide to COBOL, equipping you with the essential knowledge to understand, analyze, and even contribute to legacy COBOL systems. Whether you’re a seasoned developer or just starting, we’ll demystify COBOL and show you how it fits into the modern IT landscape.
This section outlines COBOL’s structure and syntax, essential for analyzing legacy systems, extracting business logic, and planning modernization strategies. AI-powered tools leverage this understanding to automatically extract business rules, identify code patterns, and generate modern code equivalents.
COBOL programs are organized into four Divisions.
IDENTIFICATION DIVISION.
PROGRAM-ID. EXAMPLE-PROGRAM.
* Identifies the program
ENVIRONMENT DIVISION.
* Specifies system environment (files, hardware)
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-COUNTER PIC 9(2) VALUE 0. * Defines program data
PROCEDURE DIVISION.
DISPLAY 'Hello, World!'. * Contains program logic
STOP RUN. * Ends execution
Let’s examine each division:
The IDENTIFICATION DIVISION provides program metadata, valuable for version control systems and automated analysis tools to track changes. PROGRAM-ID is mandatory.
IDENTIFICATION DIVISION.
PROGRAM-ID. SAMPLE-PROGRAM. *> Program Name (Mandatory)
AUTHOR. John Doe. *> Documentation: Author
INSTALLATION. Your Company. *> Documentation: Where it runs
DATE-WRITTEN. YYYY-MM-DD. *> Documentation: Creation date
SECURITY. Confidential. *> Documentation: Security level
The ENVIRONMENT DIVISION historically linked the program to its operating environment, specifying compilation and execution details. While crucial for hardware-specific configurations in the past, modern COBOL environments abstract away much of this complexity. The INPUT-OUTPUT SECTION remains relevant, mapping logical file names (SELECT) to physical system files (ASSIGN), which is vital for understanding data sources and destinations for data migration and integration efforts.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. COMPILER-INDEPENDENT. *> Where code was written
OBJECT-COMPUTER. COMPILER-INDEPENDENT. *> Where code runs
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT INPUT-FILE *> Logical name used in program
ASSIGN TO DISK1. *> Maps to physical device/dataset
SELECT OUTPUT-FILE
ASSIGN TO PRINTER.
The DATA DIVISION defines all data items: variables, record structures, and file layouts. It’s critical for understanding data handling and planning data migration. The FILE SECTION defines record structures within external files (using FD - File Description). The WORKING-STORAGE SECTION defines program variables. Data definition uses level numbers (e.g., 01, 05) and PICTURE (PIC) clauses for type and size. Understanding data structures in the WORKING-STORAGE SECTION is critical for AI-powered tools that analyze data flows and dependencies.
DATA DIVISION.
FILE SECTION.
FD INPUT-FILE. *> File Description for INPUT-FILE
01 INPUT-RECORD PIC X(80). *> Defines structure of records in INPUT-FILE
WORKING-STORAGE SECTION.
01 CUSTOMER-RECORD. *> A group data item (like a struct)
05 CUSTOMER-NAME PIC X(30). *> Alphanumeric field, 30 chars
05 CUSTOMER-ID PIC 9(9). *> Numeric field, 9 digits
05 BALANCE PIC 9(7)V99. *> Numeric, 7 digits before implied decimal, 2 after
The PROCEDURE DIVISION contains the executable code, holding core business logic requiring analysis. It’s organized into Paragraphs (labels ending in a period), grouping statements. It uses English-like Verbs (commands) like OPEN, READ, MOVE, ADD, IF, PERFORM, DISPLAY, CLOSE, and STOP RUN.