This paper introduces a variable classification technique to support the maintenance of COBOL application systems. It classifies program variables according to what domain entities they represent. It supports various types of software maintenance. In a system modification, it is necessary to identify the source code related to the problem at hand properly. This maintenance phase, called the impact analysis, involves significant costs in large-scale business application systems. The variable classification presented here supports finding all variables to be checked and modified. In a system restructuring, the variable classification is needed to restructure data declarations. The behavior of the classification can be changed interactively with several parameters. This paper also presents these parameters and how to set them for each type of maintenance task.