ENVIRONMENT DIVISION

SOURCE-COMPUTER Paragraph

Identifies the computer on which the program is compiled:

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SOURCE-COMPUTER. computer-name [WITH DEBUGGING MODE].

The WITH DEBUGGING MODE clause activates debugging lines in the source code (lines with 'D' in column 7).

OBJECT-COMPUTER Paragraph

Identifies the computer on which the program will be executed:

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OBJECT-COMPUTER. computer-name
    [MEMORY SIZE IS integer {WORDS|CHARACTERS|MODULES}]
    [PROGRAM COLLATING SEQUENCE IS alphabet-name]
    [SEGMENT-LIMIT IS segment-number].

• MEMORY SIZE - Rarely used in modern COBOL; historically specified available memory
• PROGRAM COLLATING SEQUENCE - Specifies the collating sequence for comparisons
• SEGMENT-LIMIT - Historical feature related to overlay structures

SPECIAL-NAMES Paragraph

Establishes relationships between system names and user-defined names, and defines special features:

• Currency sign specification
• Decimal point definition
• Symbolic characters
• Class definitions
• Alphabet definitions

FILE-CONTROL Paragraph

The FILE-CONTROL paragraph contains SELECT statements that define each file used by the program:

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FILE-CONTROL.
    SELECT [OPTIONAL] file-name
    ASSIGN TO external-name
    [ORGANIZATION IS {SEQUENTIAL|INDEXED|RELATIVE}]
    [ACCESS MODE IS {SEQUENTIAL|RANDOM|DYNAMIC}]
    [RECORD KEY IS data-name]
    [ALTERNATE RECORD KEY IS data-name [WITH DUPLICATES]]
    [FILE STATUS IS data-name].

Key FILE-CONTROL Clauses

• SELECT - Associates an internal file name (used in the program) with an external file
• ASSIGN TO - Specifies the external file name or device
• ORGANIZATION IS - Defines the file organization (SEQUENTIAL, INDEXED, or RELATIVE)
• ACCESS MODE IS - Specifies how records will be accessed (SEQUENTIAL, RANDOM, or DYNAMIC)
• RECORD KEY IS - Identifies the key field for indexed files
• ALTERNATE RECORD KEY IS - Defines additional keys for indexed files
• FILE STATUS IS - Names a two-character data item that will contain the file operation status code

Example: Sequential File

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SELECT TRANSACTION-FILE
    ASSIGN TO TRANFILE
    ORGANIZATION IS SEQUENTIAL
    ACCESS MODE IS SEQUENTIAL
    FILE STATUS IS WS-TRANS-STATUS.

Example: Indexed File

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SELECT CUSTOMER-MASTER
    ASSIGN TO CUSTMAST
    ORGANIZATION IS INDEXED
    ACCESS MODE IS DYNAMIC
    RECORD KEY IS CUST-ID
    ALTERNATE RECORD KEY IS CUST-NAME WITH DUPLICATES
    FILE STATUS IS WS-CUST-STATUS.

SEQUENTIAL Organization

Records are stored in physical order, one after another:

• Must be processed in order from beginning to end
• No direct access to specific records
• Suitable for batch processing where all records are processed
• Examples: transaction logs, report files

INDEXED Organization

Records are referenced through an index based on key values:

• Records can be accessed directly using key values
• Requires at least one key field (RECORD KEY)
• Can have multiple access paths (ALTERNATE RECORD KEY)
• Typically implemented as VSAM KSDS on mainframes
• Examples: customer master files, inventory files

RELATIVE Organization

Records are identified by their position in the file:

• Records are accessed by relative record number
• Allows for "slots" that may be empty or filled
• Typically implemented as VSAM RRDS on mainframes
• Examples: array-like data structures, fixed-slot applications

SEQUENTIAL Access

Records are accessed in the order they appear in the file:

• Available for all file organizations
• Only mode available for sequential organization
• Records are processed in order by primary key for indexed files
• Records are processed in order by record number for relative files

RANDOM Access

Records are accessed directly based on key value or record number:

• Available for indexed and relative organizations
• Requires key value (indexed) or relative record number (relative)
• No need to read through the file sequentially
• Cannot use START operation for positioning

DYNAMIC Access

Combines capabilities of sequential and random access:

• Available for indexed and relative organizations
• Program can switch between sequential and random access
• Supports START operation for positioning
• Most flexible access mode

Mainframe Implementations

IBM mainframe environments have specific considerations:

• External file names in the ASSIGN clause often refer to DD names in JCL
• VSAM files (KSDS, ESDS, RRDS) correspond to indexed, sequential, and relative organizations
• Special handling for CICS and IMS/DB environments
• Device references like SYSIN, SYSOUT for standard input/output

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SELECT CUSTOMER-FILE
    ASSIGN TO CUSTFILE  *> References DD name in JCL

UNIX/Linux/Windows Implementations

Distributed platforms often use different approaches:

• External file names may reference actual filenames with paths
• Environment variables may be used to define file locations
• Special syntax for file naming based on compiler vendor

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SELECT CUSTOMER-FILE
    ASSIGN TO "/data/customers.dat"  *> Direct file path reference

Micro Focus COBOL Example

Micro Focus has its own conventions for file assignments:

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SELECT CUSTOMER-FILE
    ASSIGN TO EXTERNAL CUSTFILE  *> Name resolved at runtime

GnuCOBOL Example

GnuCOBOL uses its own approach to file assignments:

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SELECT CUSTOMER-FILE
    ASSIGN TO DYNAMIC WS-FILENAME  *> Filename in a variable