IBM Tivoli NetView for z/OS Programming: Pipes - IBM notice

Device drivers are stages that interact with devices or other system resources. They
are used to get data into or out of the pipeline.
Filters work on data already in the pipeline.
Device Drivers
When we speak of device drivers, we define a device loosely as a disk file, a
terminal, a command procedure variable, or the system environment. Although not
all of these are true devices, they all are entities with which a device driver
interacts to read or write data.
Filters
Device drivers do not act on data; they merely transport it. In general, device
drivers write their input stream to their output stream.
The simplest pipeline consists of two device drivers. Data read from one device
moves through the pipeline to the other device, as shown in Figure 11.
File
containing
test data
This PIPE command performs the functions shown in Figure 11.
PIPE < TESTDATA | CONSOLE
< TESTDATA CONSOLE
Figure 11. Map of a Pipeline with Two Device Drivers
Introduction and Concepts
The < (From Disk) stage reads data from DASD into the pipeline where each
record becomes a message, receiving the attributes of a message. Then the < (From
Disk) stage writes each message to its output stream. In Figure 11, the output of
the < stage is the input of the CONSOLE stage. The CONSOLE stage reads the
messages from its input stream, displays them on the screen and copies them to its
output stream, if one exists.
Device drivers get data into and out of a pipeline; filters, also known as selection
stages, work on data (that is, messages) already in the pipeline. Therefore, a filter
must be used with at least two device drivers: one to provide the input stream to
the filter and one to receive the output stream from the filter.
Chapter 1. NetView Pipelines Introduction and General Concepts 11