PURPOSE: To execute an another task in an application program by forming a temporary data set when the application program fails the allocation processing of a certain data set or its open processing.

CONSTITUTION: Prior to the execution of tasks 8-A, 8-B, 8-C, a task 8-D requests the opening of resources A, B, C to a resource open processing mechanism 2. If the opening of the resource C is failed, the application program 1 is abnormally ended. In order to operate the fallback of the application program, a temporary resource X is formed in stead of the resource C in question at first. To form the temporary resource X, an operator inputs the variable resister serial number of the variable resister 7-X for forming the temporary source X, the name of a skimmer 9 defining the the resouce C in question and SWITCH(DS) command designating the name of the resouce C in question from a console 5. After the preparation and registration processing of the resource X is carried, the operator executes the application program 1 again.