The Project | About Us | Contribute | Donations | License
HOME My courses Completed
◄ Previous
◄

Defining Data Sets

Next ►
►

In this section, we will explore how to define data sets in JCL. Data sets are fundamental components in JCL as they represent files or collections of data that jobs process. Understanding how to define and manage data sets is crucial for efficient job control and data handling.

Key Concepts

  1. Data Set Types:

    • Sequential Data Sets: Linear data storage, accessed sequentially.
    • Partitioned Data Sets (PDS): Collections of members, each member is like a separate file.
    • VSAM Data Sets: Virtual Storage Access Method, used for high-performance data access.

  2. Data Set Naming Conventions:

    • Must follow specific rules, such as being 1-44 characters long, using alphanumeric characters, and periods to separate qualifiers.

  3. DD Statement:

    • The DD (Data Definition) statement is used to define data sets in JCL.

Basic Structure of a DD Statement

A DD statement typically includes the following parameters:

  • DSN: Data Set Name
  • DISP: Disposition (status and handling of the data set)
  • UNIT: Device type
  • SPACE: Space allocation
  • DCB: Data Control Block (attributes of the data set)

Example of a DD Statement

//MYDATA   DD  DSN=MY.DATA.SET, 
//             DISP=(NEW,CATLG,DELETE), 
//             UNIT=SYSDA, 
//             SPACE=(CYL,(5,1)), 
//             DCB=(RECFM=FB,LRECL=80,BLKSIZE=800)

Explanation

  • DSN=MY.DATA.SET: Specifies the name of the data set.
  • DISP=(NEW,CATLG,DELETE): Indicates that the data set is new, should be cataloged if the job completes successfully, and deleted if the job fails.
  • UNIT=SYSDA: Specifies the type of device (SYSDA is a common device type).
  • SPACE=(CYL,(5,1)): Allocates space in cylinders, with primary allocation of 5 cylinders and secondary allocation of 1 cylinder.
  • DCB=(RECFM=FB,LRECL=80,BLKSIZE=800): Defines the data set's record format (Fixed Block), logical record length (80), and block size (800).

Practical Examples

Example 1: Defining a Sequential Data Set

//SEQDATA  DD  DSN=SEQ.DATA.SET, 
//             DISP=(NEW,CATLG,DELETE), 
//             UNIT=SYSDA, 
//             SPACE=(TRK,(10,5)), 
//             DCB=(RECFM=FB,LRECL=100,BLKSIZE=1000)

Example 2: Defining a Partitioned Data Set (PDS)

//PDSDATA  DD  DSN=PDS.DATA.SET, 
//             DISP=(NEW,CATLG,DELETE), 
//             UNIT=SYSDA, 
//             SPACE=(CYL,(2,1,10)), 
//             DCB=(RECFM=FB,LRECL=80,BLKSIZE=800)

Example 3: Defining a VSAM Data Set

//VSAMDATA DD  DSN=VSAM.DATA.SET, 
//             DISP=(NEW,CATLG,DELETE), 
//             UNIT=SYSDA, 
//             SPACE=(CYL,(10,5)), 
//             DCB=(RECFM=VB,LRECL=256,BLKSIZE=2560)

Exercises

Exercise 1: Define a Sequential Data Set

Task: Write a DD statement to define a new sequential data set named USER.SEQ.DATA with the following specifications:

  • Allocate 15 tracks initially and 5 tracks as secondary allocation.
  • Use a fixed block record format with a logical record length of 120 and a block size of 1200.
  • The data set should be cataloged if the job completes successfully and deleted if it fails.

Solution:

//SEQDATA  DD  DSN=USER.SEQ.DATA, 
//             DISP=(NEW,CATLG,DELETE), 
//             UNIT=SYSDA, 
//             SPACE=(TRK,(15,5)), 
//             DCB=(RECFM=FB,LRECL=120,BLKSIZE=1200)

Exercise 2: Define a Partitioned Data Set (PDS)

Task: Write a DD statement to define a new PDS named USER.PDS.DATA with the following specifications:

  • Allocate 3 cylinders initially and 2 cylinders as secondary allocation.
  • Use a fixed block record format with a logical record length of 80 and a block size of 800.
  • The data set should be cataloged if the job completes successfully and deleted if it fails.

Solution:

//PDSDATA  DD  DSN=USER.PDS.DATA, 
//             DISP=(NEW,CATLG,DELETE), 
//             UNIT=SYSDA, 
//             SPACE=(CYL,(3,2)), 
//             DCB=(RECFM=FB,LRECL=80,BLKSIZE=800)

Common Mistakes and Tips

  • Incorrect Data Set Names: Ensure the data set names follow the naming conventions.
  • Improper Space Allocation: Allocate sufficient space to avoid job failures due to space issues.
  • DCB Parameters: Ensure the DCB parameters match the data set's intended use.

Conclusion

In this section, we covered the basics of defining data sets in JCL, including the types of data sets, the structure of DD statements, and practical examples. Understanding how to define data sets correctly is essential for efficient job control and data management. In the next section, we will delve into temporary data sets and their usage in JCL.

◄ Previous
◄
Next ►
►
The Project | About Us | Contribute | Donations | License
© Copyright 2024. All rights reserved