Access method services

Access Method Services are generally known by the name IDCAMS on MVS. For more information, see z/OS DFSMS Access Method Services Commands.

Before a VSAM data set is used for the first time, its structure is defined to the system by the Access Method Services DEFINE CLUSTER command. This command defines the type of VSAM data set, its structure, and the space it requires.

Before a VSAM alternate index is used for the first time, its structure is defined to the system by the Access Method Services DEFINE ALTERNATEINDEX command. To enable access to the base cluster records through the alternate index, use the DEFINE PATH command. Finally, to build the alternate index, use the BLDINDEX command.

When you have built the alternate index, you call fopen() and specify the PATH in order to access the base cluster through the alternate index. Do not use fopen() to access the alternate index itself.

Note: You cannot use the BLDINDEX command on an empty base cluster.