KNOW ABOUT COBOL:
History of COBOL:
• COBOL (
Common Business Oriented Language) was one of the earliest high-level
programming languages.
· COBOL was developed in 1959 by the Conference on Data Systems Languages
(CODASYL). This committee was a formed by a joint effort of industry, major universities,
and the United States Government. This committee completed the specifications for COBOL
as the year of 1959 came to an end. These were then approved by the Executive Committee
in January 1960, and sent to the government printing office, which edited and printed these
specifications as Cobol60. COBOL was developed within a six month period, and yet is still
in use over 40 years later.
· Since 1960, the American National Standards Institute (ANSI) was responsible for
developing new COBOL standards.
• Three ANSI standards for COBOL have been produced: in 1968, 1974 and 1985.
• Object-oriented COBOL is the fourth edition in the continuing evolution of ANSI/ISO
standard COBOL.
· The government contributed to COBOL’s initial popularity by insisting that computers sold
or leased to the government had to have COBOL software available.
Underlining Philosophy:
•Like the name suggests, COBOL was meant to be ‘common’ or compatible among a significant
group of manufacturers. i.e. COBOL is non-proprietary .
•COBOL is designed for developing business, typically file-oriented, applications, and is not
designed for writing systems programs.
Characteristics of COBOL applications
COBOL applications can be very large, with typically more than 1,000,000 lines of code.
COBOL applications are also very long-lived. Because of the huge investment in building
COBOL applications of a million+ lines, these applications cannot be abandoned whenever a
new technology or programming language becomes popular. This is why business applications
between 10 and 30 years old are common. This is also why most of the applications affected by
the Y2K problem were in COBOL (12,000,000 COBOL applications vs. 375,000 C and C++
applications in the US alone - Jones, Capers - The global economic impact of the year 2000
software problem (Jan, 1997)
Advantages
-Simple
-Portable
-Maintainable
Disadvantages
-very wordy
-very rigid format
-not designed to handle scientific applications
Areas of application:
COBOL applications often run in critical areas of business. For instance, over 95% of
finance–insurance data is processed with COBOL (Arranga et al - In COBOL's Defense:
Roundtable Discussion (March/April 2000) - IEEE Software). This is why there was so much
panic over the year 2000 problem.
Is COBOL still used?
According to a report from Gartner group,
In 1997 they estimated that there were about 300 billion lines of computer code in use in the
world. Of that they estimated that about 80% (240 billion lines) were in COBOL and 20% (60
billion lines) were written in all the other computer languages combined (Brown, Gary DeWard -
COBOL: The failure that wasn't - COBOLReport.com)
In 1999 they reported that over 50% of all new mission-critical applications were still being done
in COBOL and their recent estimates indicate that through 2004-2005 15% of all new
applications (5 billion lines) will be developed in COBOL while 80% of all deployed
applications will include extensions to existing legacy (usually COBOL) programs.
Distinct Features of COBOL:
• The language is simple
• No pointers
• No user defined types
• No user defined functions
• ‘Structure like’ data types
• File records are also described with great detail, as are lines to be output to a printer
• COBOL is self documenting
Structure of COBOL:
COBOL programs are hierarchical in structure. Each element of the hierarchy consists of one or
more subordinate elements. The levels of hierarchy are Divisions, Sections, Paragraphs,
Sentences and Statements. There are 4 main divisions and each division provides an essential
part of the information required by the complier. At the top of the COBOL hierarchy are the
four divisions. The sequence in which they are specified is fixed, and must follow the order:
-
IDENTIFICATION DIVISION supplies information about the program to the
programmer and the compiler.
-
ENVIRONMENT DIVISION is used to describe the environment in which the program
will run.
-
DATA DIVISION provides descriptions of the data-items processed by the program.
-
PROCEDURE DIVISION contains the code used to manipulate the data described in
the DATA DIVISION. It is here that the programmer describes his algorithm.
Some COBOL compilers require that all the divisions be present in a program while others
only require the IDENTIFICATION DIVISION and the PROCEDURE DIVISION.
HelloWorld Example
000100 IDENTIFICATION DIVISION.
000200 PROGRAM-ID. HELLOWORLD.
000300
000400 ENVIRONMENT DIVISION.
000500 CONFIGURATION SECTION.
000600 SOURCE-COMPUTER. RM-COBOL.
000700 OBJECT-COMPUTER. RM-COBOL.
000800
000900 DATA DIVISION.
001000 FILE SECTION.
001100
101200 PROCEDURE DIVISION.
101300
101400 MAIN-LOGIC SECTION.
101500 DISPLAY "Hello world!"
101600 STOP RUN.
Data Types in COBOL:
•COBOL is not a strongly typed language
•
In COBOL, there are only three data types
-numeric
-alphanumeric (text/string)
-alphabetic
•Data types are declared using:
A level number.
A data-name or identifier.
A Picture clause.
•e.g. 01 GrossPay PIC 9(5)V99 VALUE ZEROS.
Group Items
•Group items are the COBOL equivalent of structures.
•The items with a group item must be elementary items or other group items.
•Ultimately every group item should be defined in terms of elementary items.
•The hierarchy in a group item is represented by different level numbers
e.g. 01 DateOfBirth.
02 DayOfBirth PIC 99.
02 MonthOfBirth PIC 99.
02 YearOfBirth PIC 9(2).
Basic Commands in COBOL:
ADD a TO b.
ADD a TO b GIVING c.
SUBTRACT a FROM b.
SUBTRACT a FROM b GIVING c.
MULTIPLY a BY b.
MULTIPLY a BY b GIVING c.
DIVIDE a INTO b.
DIVIDE a INTO b GIVING c.
COMPUTE x = a + b * c.
MOVE a TO b c.
SORT sort-file
ON ASCENDING KEY k
USING inventory-file
GIVING sorted-inventory-file .
MERGE merge-work-file
ON ASCENDING KEY K
USING input-file1 input-file2
GIVING output-file .
DISPLAY total-cost.
ACCEPT identifier.
PERFORM paragraphname1 THROUGH paragraphname2
VARYING index FROM value1 BY value2
UNTIL condition.
A detailed example in COBOL
000010 IDENTIFICATION DIVISION.
000020 PROGRAM-ID. SAMPLE.
000030 AUTHOR. J.P.E. HODGSON.
000040 DATE-WRITTEN. 4 February 2000
000041
000042* A sample program just to show the form.
000043* The program copies its input to the output,
000044* and counts the number of records.
000045* At the end this number is printed.
000046
000050 ENVIRONMENT DIVISION.
000060 INPUT-OUTPUT SECTION.
000070 FILE-CONTROL.
000080 SELECT STUDENT-FILE ASSIGN TO SYSIN
000090 ORGANIZATION IS LINE SEQUENTIAL.
000100 SELECT PRINT-FILE ASSIGN TO SYSOUT
000110 ORGANIZATION IS LINE SEQUENTIAL.
000120
000130 DATA DIVISION.
000140 FILE SECTION.
000150 FD STUDENT-FILE
000160 RECORD CONTAINS 43 CHARACTERS
000170 DATA RECORD IS STUDENT-IN.
000180 01 STUDENT-IN PIC X(43).
000190
000200 FD PRINT-FILE
000210 RECORD CONTAINS 80 CHARACTERS
000220 DATA RECORD IS PRINT-LINE.
000230 01 PRINT-LINE PIC X(80).
000240
000250 WORKING-STORAGE SECTION.
000260 01 DATA-REMAINS-SWITCH PIC X(2) VALUE SPACES.
000261 01 RECORDS-WRITTEN PIC 99.
000270
000280 01 DETAIL-LINE.
000290 05 FILLER PIC X(7) VALUE SPACES.
000300 05 RECORD-IMAGE PIC X(43).
000310 05 FILLER PIC X(30) VALUE SPACES.
000311
000312 01 SUMMARY-LINE.
000313 05 FILLER PIC X(7) VALUE SPACES.
000314 05 TOTAL-READ PIC 99.
000315 05 FILLER PIC X VALUE SPACE.
000316 05 FILLER PIC X(17)
000317 VALUE 'Records were read'.
000318 05 FILLER PIC X(53) VALUE SPACES.
000319
000320 PROCEDURE DIVISION.
000321
000330 PREPARE-SENIOR-REPORT.
000340 OPEN INPUT STUDENT-FILE
000350 OUTPUT PRINT-FILE.
000351 MOVE ZERO TO RECORDS-WRITTEN.
000360 READ STUDENT-FILE
000370 AT END MOVE 'NO' TO DATA-REMAINS-SWITCH
000380 END-READ.
000390 PERFORM PROCESS-RECORDS
000410 UNTIL DATA-REMAINS-SWITCH = 'NO'.
000411 PERFORM PRINT-SUMMARY.
000420 CLOSE STUDENT-FILE
000430 PRINT-FILE.
000440 STOP RUN.
000450
000460 PROCESS-RECORDS.
000470 MOVE STUDENT-IN TO RECORD-IMAGE.
000480 MOVE DETAIL-LINE TO PRINT-LINE.
000490 WRITE PRINT-LINE.
000500 ADD 1 TO RECORDS-WRITTEN.
000510 READ STUDENT-FILE
000520 AT END MOVE 'NO' TO DATA-REMAINS-SWITCH
000530 END-READ.
000540
000550 PRINT-SUMMARY.
000560 MOVE RECORDS-WRITTEN TO TOTAL-READ.
000570 MOVE SUMMARY-LINE TO PRINT-LINE.
000571 WRITE PRINT-LINE.
000572
000580
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