An AMS (Access Method Service) is a service program that performs a wide range of functions on VSAM/Non-VSAM datasets and catalogues. AMS includes a powerful utility program known as IDCAMS that can be invoked via a standard JCL and is able to carry out a slew of AMS functions through its commands. AMS deploys two kinds of commands:
Functional commands: These are commands that demand real action, like DEFINE CLUSTER, REPRO, VERIFY, DELETE, BLDINDEX, and LISTCAT.
Modal commands: These are commands that specify conditions for executing functional commands such as "IF-THEN-ELSE". A TSO (Time Sharing Option) user can only use functional commands, not modal commands.
