Understanding DATA Step Processing (1)

Debugging and Testing DATA Steps

Understanding DATA Step Processing

This section teaches you how SAS processes a DATA step. Understanding this process will help you in writing and debugging DATA step programs. After completing this section, you will be able to

identify the two phases in DATA step processing
define the program data vector
name the default actions that occur at the end of a DATA step.

When you submit a DATA step, SAS processes the DATA step in two distinct phases:

Descriptor and Data Portions of Data Set

During the compilation phase, the descriptor portion of the data set is created and each statement is scanned for syntax errors. Most syntax errors prevent further processing of the DATA step.
If the DATA step compiles successfully, then the execution phase begins. A DATA step executes once for each observation in the input data set, unless otherwise directed. This creates the data portion of the data set.

First, let's look at the compilation phase.