Types of symbols

There are two types of symbols that you can specify in application or vendor programs:

System symbols are defined to the system at initialization. Your installation specifies substitution texts for system symbols or accepts their default values. When a program calls ASASYMBM, it can accept the installation-defined substitution texts or override them. There are two types of system symbols:
- Static system symbols have substitution texts that are defined at system initialization and remain fixed for the life of an IPL. Static system symbols represent fixed values such as system names and sysplex names.
  The DISPLAY SYMBOLS command displays the static system symbols and associated substitution texts that are currently in effect. See z/OS MVS System Commands for details about DISPLAY SYMBOLS.
- Dynamic system symbols have substitution texts that can change at any point in an IPL. They represent values that can change often, such as dates and times. A set of dynamic system symbols is defined to the system; your installation cannot provide additional dynamic system symbols.
See the information on using system symbols in z/OS MVS Initialization and Tuning Reference for lists of dynamic and static system symbols.
User symbols are symbols that a caller defines on a call to ASASYMBM. They are valid only for the specific call. The caller specifies the names and substitution texts for user symbols in a symbol table. If the names of user symbols are the same as the names of system symbols, the substitution texts for the user symbols override the substitution texts for the system symbols.

If your program accepts the substitution texts for the installation-defined system symbols, there is no need to specify those system symbols in the symbol table that you provide to ASASYMBM; substitution for those system symbols is performed automatically. However, if your program wants to override the installation-defined substitution texts for system symbols, you must specify those system symbols in the symbol table. The symbol table is the only place where you can specify user symbols.