SPSS® 12.0 Command Syntax Reference

Appendix A
Commands and Program States
Command order is determined only by the system’s need to know and do certain
things in logical sequence. You cannot label a variable before the variable exists in
the file. Similarly, you cannot transform or analyze data before a working data file is
defined. This appendix briefly describes how the program handles various tasks in a
logical sequence. It is not necessary to understand the program states in order to
construct a command file, but some knowledge of how the program works will help
you considerably when you encounter a problem or try to determine why the program
doesn’t seem to want to accept your commands or seems to be carrying out your
instructions incorrectly.
Program States
To run a program session, you need to define your working data file, transform the data,
and then analyze it. This order conforms very closely to the order the program must
follow as it processes your commands. Specifically, the program checks command order
according to the program state through which it passes. The program state is a characteristic
of the program before and after a command is encountered. There are four
program states. Each session starts in the initial state, followed by the input program
state, the transformation state, and the procedure state. The four program states in
turn enable the program to set up the environment, read data, modify data, and execute
a procedure. Figure A.1 shows how the program moves through these states. The
program determines the current state from the commands that it has already encountered
and then identifies which commands are allowed in that state.
Figure A.1 Program states
Initial
Setup
Input
Program
1687
Transformation
Program
Procedure Finish