Before you can use IMS TM or IMS DB, you must define the elements and functions that make up the IMS system, including:

• Databases
• Application programs
• Terminals
• All optional features of IMS, including the type of control region that is required (DB/DC, DBCTL, DCCTL)
• Security

IMS provides macros and procedures that enable you to define your system. IMS also provides user exits that enable you to customize processing. A user exit is the point in IMS's code at which an exit routine can be given control.

To define an IMS system, you can either customize the sample IMS system that is verified with the IVP (see IMS Installation Verification Program (IVP) ) or copy the sample IMS system and customize the copy for your installation.

Related Reading: For more information about the IMS definition process, see The IMS System Definition Process.

Setting up security for the IMS system is also part of the system definition process. IMS has its own built-in security functions and can provide more extensive security through employing user-written exit routines, a security product (such as RACF), or both.

Related Reading: For more information about IMS security, see the complete version of An Introduction to IMS. For complete information about IMS security, see the IMS Security.