Your PL/I programs can process and transmit units of information called records. A collection of records is called a data set, but for PL/I workstation products, a data set can be either a file or a device. Data sets are logical collections of information external to PL/I programs; they can be created, accessed, or modified by programs written in PL/I.
Your PL/I program recognizes and processes information in a data set by associating it with a symbolic representation of the data set called a PL/I file. This PL/I file represents the environment independent characteristics of a set of input and output operations.
In order to minimize confusion, this book uses the term PL/I file to refer to the file declared and used in a PL/I program. The terms data set and workstation file (or workstation device) are used to refer to the collection of data on an external I/O device. In some cases the data sets have no name; they are known to the system by the device on which they exist.