Your PL/I programs process and transmit units of information called records. A collection of records is called a data set. Data sets are physical collections of information external to PL/I programs; they can be created, accessed, or modified by programs written in PL/I or other languages or by the utility programs of the operating system.
Your PL/I program recognizes and processes information in a data set by using a symbolic or logical representation of the data set called a file. This chapter describes how to associate data sets with the files known within your program. It introduces the five major types of data sets, how they are organized and accessed, and some of the file and data set characteristics you need to know how to specify.