DSN Parameter

Purpose

The DSN (or DSNAME) parameter specifies the name of a data set that a job step is creating or accessing. It identifies the specific data set to be allocated or processed by the program. The DSN parameter is one of the most fundamental parameters on the DD statement, as it establishes the connection between a program and the data it needs to process.

Syntax

Basic Syntax

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//ddname DD DSN=dataset.name,other-parameters
//ddname DD DSNAME=dataset.name,other-parameters

Temporary Data Set

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//ddname DD DSN=&&tempname,other-parameters

Member of a Partitioned Data Set

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//ddname DD DSN=dataset.name(member),other-parameters

Generation Data Group

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//ddname DD DSN=gdg.name(+1),other-parameters
//ddname DD DSN=gdg.name(0),other-parameters
//ddname DD DSN=gdg.name(-1),other-parameters

Format

Data Set Name Rules

• Length: 1-44 characters (including periods)
• Qualifiers: 1-8 characters separated by periods
• Valid characters: Alphanumeric (A-Z, 0-9), national characters (@, #, $), hyphen (-)
• First character: Alphabetic (A-Z) or national character (@, #, $)
• Qualifier structure: dataset.name.qualifier1.qualifier2...
• Maximum qualifiers: Usually 22 (with 21 periods)

Special Format Variations

Examples

Basic Data Set Reference

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//INFILE  DD DSN=SYS1.PAYROLL.DATA,DISP=SHR

Refers to the cataloged data set SYS1.PAYROLL.DATA

Creating a New Data Set

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//OUTFILE DD DSN=USER.NEW.DATASET,
//            DISP=(NEW,CATLG,DELETE),
//            SPACE=(CYL,(10,5)),
//            DCB=(RECFM=FB,LRECL=80,BLKSIZE=27920)

Creates a new data set USER.NEW.DATASET with the specified attributes

Temporary Data Set

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//TEMPFILE DD DSN=&&TEMPDS,
//            DISP=(NEW,DELETE),
//            SPACE=(TRK,(5,1)),
//            DCB=(RECFM=FB,LRECL=80,BLKSIZE=800)

Creates a temporary data set that exists only for the duration of the job

Accessing a PDS Member

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//MEMBER   DD DSN=SYS1.PARMLIB(IEAIPS00),DISP=SHR

Refers to member IEAIPS00 in the partitioned data set SYS1.PARMLIB

Creating a New Generation

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//GDGFILE  DD DSN=PROD.SALES.DATA(+1),
//            DISP=(NEW,CATLG,DELETE),
//            SPACE=(CYL,(50,10)),
//            DCB=(RECFM=FB,LRECL=200,BLKSIZE=27800)

Creates a new generation (+1) in the GDG PROD.SALES.DATA

Data Set Concatenation

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//INPUTALL DD DSN=PROD.CURRENT.DATA,DISP=SHR
//         DD DSN=PROD.HISTORY.DATA,DISP=SHR
//         DD DSN=PROD.ARCHIVE.DATA,DISP=SHR

Concatenates three data sets to be processed sequentially by the program

Data Set Reference Back

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//STEP1    EXEC PGM=SORT
//SORTIN   DD DSN=INPUT.DATA,DISP=SHR
//SORTOUT  DD DSN=SORTED.DATA,DISP=(NEW,CATLG,DELETE),
//            SPACE=(CYL,(10,5)),DCB=(*.SORTIN)
//STEP2    EXEC PGM=REPORT
//INPUT    DD DSN=*.STEP1.SORTOUT,DISP=SHR

STEP2 refers back to the data set created in STEP1

Special DSN Formats

Backward References

Temporary Data Sets

Temporary data sets are identified using double ampersands (&&) and exist only for the duration of the job. They are automatically deleted at the end of the job.

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//TEMP    DD DSN=&&TEMPDS,DISP=(NEW,PASS),SPACE=(TRK,(1,1))
//STEP2   EXEC PGM=PROG2
//INPUT   DD DSN=&&TEMPDS,DISP=(OLD,DELETE)

System-Generated Names

If DSN is omitted for a NEW data set, the system generates a unique name. This is not recommended for most situations as it makes the data set difficult to identify.

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//SYSUT1  DD DISP=(NEW,DELETE),SPACE=(TRK,(1,1))  // System-generated name

DSN with Symbolic Parameters

Data set names can include symbolic parameters that are resolved during job execution.

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//PROCSTEP PROC DATE=20230101
//OUTFILE  DD DSN=PROD.DATA.D&DATE,DISP=(NEW,CATLG,DELETE),
//            SPACE=(CYL,(10,5))
//         PEND
//*
//STEP1    EXEC PROCSTEP,DATE=20240515

The final data set name would be PROD.DATA.D20240515

Use Cases

Common Patterns

Limitations

• Length: Maximum 44 characters for the entire data set name
• Qualifier length: Maximum 8 characters per qualifier (segment between periods)
• Character restrictions: Limited to alphanumeric, national characters, and hyphens
• First character: Must be alphabetic or national character (@, #, $), not numeric
• Reserved names: Some names are reserved by the system and cannot be used
• Uniqueness: Data set names must be unique within a catalog structure
• GDG limitations: Maximum of 255 generations in a GDG

Common Mistakes

• Invalid characters: Using characters not allowed in data set names
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  //INVALID DD DSN=USER.FILE-NAME!,DISP=SHR  // ! is not valid

• Qualifier too long: Using qualifiers over 8 characters
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  //TOOLONG DD DSN=USER.VERYLONGQUAL.DATA,DISP=SHR  // VERYLONGQUAL exceeds 8 chars

• Numeric first character: Starting a data set name with a number
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  //NUMSTART DD DSN=1DATA.FILE,DISP=SHR  // Cannot start with a number

• Single ampersand for temporary data set: Using & instead of &&
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  //BADTEMP DD DSN=&TEMP,DISP=(NEW,DELETE)  // Should be &&TEMP

• Missing member name parentheses: Incorrect specification of PDS members
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  //NOPAREN DD DSN=SYS1.PARMLIB.MEMBER1,DISP=SHR  // Should be SYS1.PARMLIB(MEMBER1)

• Forgotten period in GDG: Incorrect GDG syntax
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  //BADGDG DD DSN=ACCOUNT.MASTER+1,DISP=OLD  // Should be ACCOUNT.MASTER(+1)

Best Practices

• Consistent naming conventions: Establish and follow standard naming patterns for your data sets
• Meaningful names: Use descriptive names that reflect content or purpose
• High-level qualifiers: Use organization-wide standards for HLQs to group related data sets
• Version control: Use GDGs or date-based naming for versioned data
• Environment segregation: Include environment indicators (DEV/TEST/PROD) in data set names
• Symbolic parameters: Use symbolic parameters for date-dependent or variable components
• Documentation: Maintain documentation of naming standards and meanings
• Temporary data set management: Use && for true temporary data sets, and create appropriate dispositions
• Backward references: Use backward references to ensure consistency between steps

Related Concepts

• DD Statement - The DSN parameter is coded on the DD statement
• DISP Parameter - Controls the status and disposition of the data set
• Generation Data Groups (GDG) - For versioned data sets with relative generation numbers
• Concatenation - Combining multiple data sets logically
• Symbolic Parameters - For variable components in data set names

Related Pages

• DD Statement
• DISP Parameter
• SPACE Parameter
• UNIT Parameter
• VOLUME Parameter
• DCB Parameter