COBOL History
COBOL (Common Business Oriented Language)
was one of the earliest high-level programming
languages. It was developed in 1959 by a group of
computer professionals called the Conference on
Data Systems Languages (CODASYL). Since 1959
it has undergone several modifications and
improvements. In an attempt to overcome the
problem of incompatibility between different
versions of COBOL, the American National
Standards Institute (ANSI) developed a standard
form of the language in 1968. This version was
known as American National Standard (ANS)
COBOL.
1
In 1974, ANSI published a revised version of (ANS)
COBOL, containing a number of features that were
not in the 1968 version. In 1985, ANSI published
still another revised version that had new features
not in the 1974 standard. The language continues
to evolve today. Object-oriented COBOL is a
subset of COBOL 97, which is the fourth edition in
the continuing evolution of ANSI/ISO standard
COBOL. COBOL 97 includes conventional
improvements as well as object-oriented features.
Like the C++ programming language, objectoriented COBOL compilers are available even as
the language moves toward standardization.
2
Areas of Application
COBOL is ideally suited for the solution of business
problems. For example, if a company wanted to
keep track of its employees’ annual wages, COBOL
would be ideal language for implementation. It is
interesting to note that COBOL was the first
programming language whose use was mandated
by the Department of Defense (DoD).
3
It’s not dead!
• millions of lines of COBOL code
presently exist
• heavy need for year 2000
• new standards in ‘98
4
Introduction to COBOL
and Program Development
• COBOL –
– COmmon Business Oriented Language
• First released in 1960 by CODASYL
– Conference of Data Systems Language
• Purpose was to provide a High-Level
Programming Language for the
business world.
5
High-Level Vs. Low-Level
Languages
• High-Level Language
– The program statements are not closely
related to the internal characteristics of
the machine.
– Are more English-like and less cryptic
– Can be easily transferred from one
• Examples
– COBOL, C++, C#, Java, VB, etc.
6
High vs. Low-Level Languages+
• Low-Level Language
– Uses symbolic notation to represent
machine instructions
– Is closely related to the internal
architecture of the machine
– Cannot be transferred from, one machine
system to another
• Examples:
– Machine language, Assembly language
7
COBOL’s Survival
• COBOL is widely accepted
• Has been in use for over 35 years
• Many businesses have great
investment in COBOL programs.
• COBOL is available on every computer
platform
• Object-COBOL is available
• COBOL Versions: ’68, ’74, ’85, ’90?
8
Advantages of COBOL
• COBOL was designed to be machineindependent, English-like, and selfdocumenting
• COBOL has had ANSI support since
1960
• ANSI
– American National Standards Institute
• COBOL Compiler
– Translates COBOL source code into
machine language
9
Disadvantages of COBOL
• COBOL programs are wordy
• They are longer than those produced
in most other languages
• Is not popularly employed for coding
scientific applications
10
Information Processing
• Information Processing
– The production of information by
processing data on a computer.
• Stream Input/Output
– This is typical with C++, Java, VB, etc
– Program reads data and assigns it to
variables
• Record Input/Output
– This is typical with COBOL
– COBOL groups data into fields and
records
11
Record Blocking
• Increases the efficiency of record I/O
• Blocking
– Grouping the records transmitted from
secondary memory to the CPU as needed
by the program
– Records are supplied one at a time to the
program through READ statements
• The block is a physical record and
each record within the block is a
logical record
12
Steps in the Programming
Process
•
•
•
•
•
Understand the Problem
Design the Program
Code the Program
Test the Program
Document the Program
13
Step 1 - Understanding the
Problem
• Be sure that you have a complete
understanding of the purpose of the program
• read the specifications
• Establish and maintain a channel of
communication with the client
• Determine what the output of the program
should be
• Examine the input
• Determine what mathematical calculations
are needed
14
Step 2 - Design the Program
• Develop the sequence of steps you will
need to solve the problem
• Should not involve a computer
• Tools needed are: spacing chart,
flowcharts, hierarchy charts, and
pseudocode.
• Make use of the top-down design approach
to problem solving
15
Step
+
2
-- Design Tools
• Spacing chart
– Consists of rows and columns that can be used to
design the appearance of a screen or a printed report
• Flowchart
– A graphical representation of the steps needed to
solve a problem
• Hierarch chart
– Demonstrates the relationship between the
paragraphs used in the program and how the solution
is organized
• Pseudocode
– An English-like representation of the actions needed
to solve the problem.
16
Step 3 - Coding the Program
• Design the logic and then translate it into COBOL
code
• Source code
– These are the instructions you write for the computer to
carry out.
– It is your code before it is translated into machine
language
– You write source code with a text editor
– A language sensitive editor helps you by placing the
cursor in the correct column positions and pointing out
syntax errors
• Syntax errors –caused by not using the language
17
correctly
Step 4 - Testing the Program
• After writing the program, you need to
compile it.
• Compilation
– translating the source code (program) to
machine code
– This is done by the compiler
• If syntax errors show up, you should
correct them and recompile until you
obtain a clean compile
18
Step 5–Documenting the Program
• Documentation is necessary to allow people to
figure out how to use your program and/or fix it
when future errors show up or modifications are
necessary.
• Program documentation can take many forms:
– External documentation
• Notes and Manuals for other programmers
– Comments lines and meaningful data names
• These help with program readability and enhances
the self-documenting nature of COBOL code.
19
Structured Programming
• Structured programming uses the three basic logic
control structures:
– Sequence, selection, & iteration
• A logic control structure is a way in which
statements in a program can be executed.
• Advantages offered:
– Programs appear neater and are more readable
– Reliability and efficiency of programs are improved
– Reduces time spent on debugging, testing, and modifying
programs
– Increases programmer productivity
20
Top-Down Design/Programming
• Methodologies for solving large problems
• Top-Down Design
– Breaks a large, complex problem into smaller,
less complex units
– Also called Divide and Conquer strategy
• Top-Down Programming
– The high-level modules are coded as soon as
they are designed.
21
Divisions of a COBOL Program
• All COBOL programs are divided into four
divisions.
• IDENTIFICATION DIVISION
• ENVIRONMENT DIVISION
• DATA DIVISION
• PROCEDURE DIVISION
• Each division has a function in the overall
development and execution of the program
22
IDENTIFICATION DIVISION
• Provides the computer with basic information
about the program
• Has only one required entry
• The division header contains the reserved
words IDENTIFICATION DIVISION
• The reserved word: PROGRAM-ID is used to
name the program.
• The program name is selected by the programmer.
• Periods are required at end of each division .
23
IDENTIFICATION
+
DIVISION
• The COBOL language processor looks for
periods to terminate various elements of
the program.
• The asterisk (*) is used to convey
documentation in the program.
• Comment
– The * is placed in column 7 and is ignored by
the COBOL compiler.
24
IDENTIFICATION DIVISION
• Identifies the program
• Example
IDENTIFICATION DIVISION.
PROGRAM-ID. PRGM01.
25
ENVIRONMENT DIVISION
• This is the most hardware-dependent part of a
COBOL program
• Defines Input and Output
• Contains the INPUT-OUTPUT SECTION and the
FILE-CONTROL paragraph.
• The INPUT-OUTPUT SECTION:
– Designates the data files that the program uses.
– Each data file is associated with a hardware inputoutput device
26
2.0 ENVIRONMENT DIVISION
• There are two sections in this division
• Configuration section (Hardware details;
this section is NOT NEEDED)
• Input-Output section(File details)
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT SALES-FILE ASSIGN TO DISK.
SELECT PRNT-FILE ASSIGN TO PRINTER.
27
DATA DIVISION
• This DIVISION typically contains two sections
– FILE SECTION, and
– WORKING-STORAGE SECTION
• File section deals with Input and Output file
descriptions
– FD - File description (starts in Area A)
– 01 - to describe the record layout (also in area A)
• Working Storage section
– Is the section where the input and output records are
manipulated and all other variables needed are defined.
– Typically contains the variables, heading lines and detail
28
record
COBOL Language Elements
• In a COBOL program, you’ll find the
following words
– Words
• Reserved words
• User Defined words
– Constants or Literals
• Non-Numeric
• Numeric
• Figurative constants
– Note: Reserve words, and User Defined words
29
are case NON-sensitive
COBOL Language Elements
• Reserved words
• User Defined words
– These are data names for storage, paragraph,
and section names
– Examples:
• EMPLOYEE-NAME-OUT
• WS-END-OF-FILE-INDICATOR
30
COBOL Language Elements
– Rules:
• max 30 characters
• A-Z, 0-9, and hyphen (-)
• must start and end with A-Z, or 0-9
(paragraph ad section name are the only
user defined words that are allowed to start
with 0-9)
• cannot begin or end with hyphen
• must be at least one alphabetic character
• cannot be a reserved word
31
COBOL Language Elements
• Non-Numeric Literals
– these are string constants
– Examples:
• “Summary of Loans Report”
• “ABC”
– Rules:
• max 160 characters
• quotation marks are required before and
after (single or double - compiler option)
• contents between the quotes are casesensitive
32
COBOL Language Elements
• Numeric Literals
– these are hard-coded numbers
– Examples:
• 12.45
• -1
– Rules:
• max 18 digits
• +, - must appear on the left of the number
33
Non-Edited Picture Characters
• X Alpha-numeric (1 byte)
• 9 Numeric (1 bytes)
• S Operational SIGN (does not take up any
space)
• e.g.
05 WS-CREDIT PIC S9(3)
• V Implied Decimal Point
• e.g.
05 WS-SALARY PIC 9(5)V9(02)
34
Example Input file and File Description
Data File of SALEFILE
•
•
•
•
111111111MOOING MARTY
222222222PATSY POTATO
333333333ROWDY RODENT
444444444STARING STACEY
001451255000
450003569050
205001259020
000090000650
The File Description:
FD SALES-FILE
RECORD CONTAINS 80 CHARACTERS
DATA RECORD IS SALES-REC.
01 SALES-REC.
05 EMPLOYEE-NUM-IN
PIC 9(09).
05 NAME-IN
PIC X(20).
05 QUANTITY-IN
PIC 9(05).
05 AMOUNT-IN
PIC 9(05)V99.
05 FILLER
PIC X(39)
Note the use of X and 9 and numbers in parentheses
35
Example Input file and File Description
Main Memory
Program Executable Code
Disk
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT SALES-FILE
ASSIGN
TO DISK-SALEFLE.
DATA DIVISION.
FILE SECTION.
FD FD SALES-FILE
RECORD CONTAINS 80 CHARACTERS
DATA RECORD IS SALES-REC.
Buffer
01 SALES-REC.
05 EMPLOYEE-NUM-IN
05 NAME-IN
05 QUANTITY-IN
05 AMOUNT-IN
05 FILLER
Working Storage
SALEFLE
file
.
PIC
PIC
PIC
PIC
PIC
9(09).
X(20).
9(05).
9(05)V99.
X(39)
AS400
Operating
System
36
Working Storage Section
• Purpose
– to save, or store temporary data for use in the
program
• Records and variables
– consist of Group and Elementary items
– Elementary items MUST HAVE a PIC clause
– Group items may consist of one or more
elementary item, or other Group items
– Group items are consider alphanumeric
always
– To show groupings, LEVEL numbers are used 37
Working Storage Section
– Rules:
• In sequence (from smaller numbers to larger)
• But don’t have to be consecutive
• Also, not required to jump by any given
interval; can be random
• Record level is 01 level
• Valid numbers are 01 through 49 inclusive
• 66, 77, 88 have special purpose usage
38
Working Storage Section
– VALUE clauses are ONLY allowed in Working
Storage (not allow in FILE section).
– Used to initial elementary data items
– Cannot be used for group items
– can take a
• literal
• Figurative constant
• the word ALL
39
Working Storage Section
– Examples:
01 WS-RPT-TITLE.
05 WS-RPT-TITLE PIC X(20)VALUE
‘SALES REPORT’.
05 WS-CHRISTMAS-DAY.
10 XMAS-YR PIC 9(04) VALUE 2002.
10 XMAS-MM PIC 9(02) VALUE 12.
10 XMAS-DD PIC 9(02) VALUE 25.
01 DRAW-LINE PIC X(133) VALUE ALL “*”.
40
The PROCEDURE DIVISION
• Contains the program logic processing
steps
• Contains procedures, which are actions to
be carried out by the program
• It s made up of separate modules called
paragraphs.
• Statements in the PROCEDURE
DIVIDION begin with action verbs
41
The Paragraph Name
•
•
•
•
A paragraph name is user-defined.
It must end with a period.
No blanks are allowed in the name.
Hyphens may be used to separate the words
that make up the paragraph name.
• Recommended to start the name with a module
level number.
• Following the paragraph name are COBOL
statements – These designate operations to take
place and thus begin with verbs.
42
Overall Program Execution
• COBOL statements are not executed directly
• They are converted into machine language
• The statements in the program are called source
code
• The statements that the computer executes is
called the object code
• Execution of a program begins with the first
statement following the PROCEDURE DIVISION
and continues statement by statement until the
end of the program is encountered.
43
COBOL Coding Format
• The Coding form – this is divided into four
major fields :
Usage
Columns
Sequence numbers
1–6
Indicator area (*,-)
7
Area A (Headers)
8 – 11
Area B (statements)
12 – 72
Program identification 73 – 80
44
Program Preparation+
• Line numbers in the program are NOT
entered by the programmer. They are
generated by the compiler.
• Area A and Area B entries
– Columns 8 – 11 is area A
– Columns 12 – 72 is area B
• These columns are significant because
COBOL entries must start in specific
columns.
45
46
Procedure Division
• Its very important to be precise while dealing
with the procedure division.
• This is the only division that requires
hierarchy chart, pseudocode, and program
flowcharts.
• Hierarchy chart: Overview of the process.
• Pseudocode: Near COBOL code without
syntax.
• Flowchart: Graphical representation of
program flow.
47
Hierarchy Chart
• Level1
MAIN-RTN
• Level2 HDG-RTN
READ-RTN
• Level3
DETAIL-RTN
READ-RTN
48
Pseudocode
MAIN PROCESS
OPEN FILES
WRITE HEADINGS
READ FIRST RECORD
PROCESS RECORDS UNTIL NO MORE RECORDS
CLOSE FILES
STOP PROCESSING
WRITE HEADINGS
MOVE AND WRITE HEADING LINE 1
MOVE AND WRITE HEADING LINE 2
PROCESS RECORDS
MOVE AND WRITE DETAIL RECORDS
READ NEXT RECORD
49
F
L
O
W
C
H
A
R
T
PROGRAM
FLOW
START
OPEN FILES
READRTN
HDGRTN
UNTIL WSEOF=‘Y’
DETAILRTN
CLOSE
FILES
STOP
50
What should you do?
• Ask questions
• Read chapter
• Do exercises at end
of chapter
• Think!
• Ask questions!
51