Table pairs provide a facility to change, delete, or add to JES2 processing, function, or both. Changes made to JES2 processing using table pairs are generally less prone to error than are changes made through installation exits. This is true because JES2 macros generate the tables and generally require you to write less code to be run.

A number of JES2 functions (such as initialization statement processing, command processing, and message building) use tables. You can customize these JES2 functions, and others, by extending their associated tables. JES2 examines two tables, known as a table pair. The first table (the JES2 table) provides the default processing specifications; the second table (the user table) is used to extend, change, or delete the default processing specifications. For example, you can add your own JES2 commands and messages, add a new initialization statement or parameter, abbreviate the length of a JES2 command, or delete an unnecessary command to prevent its accidental misuse.

To simplify the use of this facility, you can use the JES2 default tables as templates for constructing your own tables. Depending on the tables that you choose to start with, using table pairs generally takes less detailed knowledge of JES2 internal structures than does writing an exit.

Table pairs do not replace the need for exits. Table pairs and exit points can provide added capability either independently or in conjunction with one another.