(1) In CICS, an index based on an alternate key. It allows the file to be processed in a secondary key order.
(2) For VSAM key-sequenced data sets and entry-sequenced data sets, an index of alternate keys that provides a path for secondary access to the data set. If the records have alternate keys, the alternate index is built when the data set is created. See also secondary index.
(3) A subordinate index in a hierarchy of indexes.
(4) In z/OS Virtual Storage Access Method (VSAM), a collection of index entries related to a given base cluster and organized by a key other than the prime key of the associated, base-cluster, data records. An alternate index provides an alternate directory for locating records in the data component of a base cluster.