If the request to START structure alter is valid, all active connectors to the structure are notified of the Structure Alter Begin event (EEPLALTERBEGIN) through their event exit. The connectors can examine the event exit parameter list (IXLYEEPL) to determine the requested target values, the ratio change indication, and the composite values for the minimum percentage of entries and/or elements and EMC storage percentage to be available. The information available in IXLYEEPL when the Structure Alter Begin event is presented is mapped by EEPLALTERBEGININFO.

If the request is to change the size of the structure, EEPLALTERSIZE contains the requested size. The connector can compare this size with that returned in IXLYCONA at connect time to determine how the size is to be altered. The connector might want to free up any in-use or in-use and changed structure resources to accommodate the alter process.

If the request is to alter a structure in the duplexing rebuild process, EEPLSTRSTATEREBUILDDUPLEX is a flag that indicates duplexing rebuild is in progress. EEPLSTRUCTUREVERSION is the structure version of the instance of the structure for which the Alter Begin event is issued. EEPLALTERBEGINDUPREBOLD or EEPLALTERBEGINDUPREBNEW identify the old or new instance of the structure that is being altered.

Connectors to the structure are not required to respond to the structure alter event.