Rational Developer for System z
Enterprise PL/I for z/OS, Version 3.8, Programming Guide

Establishing data set characteristics

Blocks and records
Information interchange codes
Record formats
Fixed-length records
Variable-length records
Undefined-length records
Data set organization
Labels
Data Definition (DD) statement
Use of the conditional subparameters
Data set characteristics
Using the TITLE option of the OPEN statement
Associating PL/I files with data sets
Opening a file
Specifying characteristics in the ENVIRONMENT attribute
The ENVIRONMENT attribute
Record formats for record-oriented data transmission
Record formats for stream-oriented data transmission
RECSIZE option
BLKSIZE option
Record format, BLKSIZE, and RECSIZE defaults
GENKEY option — key classification
SCALARVARYING option — varying-length strings
KEYLENGTH option
ORGANIZATION option
Data set types used by PL/I record I/O
Setting environment variables
PL/I standard files (SYSPRINT and SYSIN)
Redirecting standard input, output, and error devices

A data set consists of records stored in a particular format which the operating system data management routines understand. When you declare or open a file in your program, you are describing to PL/I and to the operating system the characteristics of the records that file will contain. You can also use JCL or an expression in the TITLE option of the OPEN statement to describe to the operating system the characteristics of the data in data sets or in the PL/I files associated with them.

You do not always need to describe your data both within the program and outside it; often one description will serve for both data sets and their associated PL/I files. There are, in fact, advantages to describing your data's characteristics in only one place. These are described later in this chapter and in following chapters.

To effectively describe your program data and the data sets you will be using, you need to understand something of how the operating system moves and stores data.


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