When a new data set is being allocated, the classes are selected by the Automatic Class Selection (ACS) routines which are coded by the user in a language similar to TSO CLIST. There are four types of ACS routines: three types which select each of three types of classes and one to select the candidate storage group(s) that will ultimately hold the data set. These routines have access to and can use information about the job, the user, the data set, and the environment to select the appropriate classes. However, since this suppresses the power of active selection, it is not usually recommended.
When SMS is active, all new allocations pass through the Data Class ACS routine to have the Data class assigned and then into the Storage Class ACS routine to see if a Storage class will be selected. If no Storage class is selected, the data set will not be SMS controlled and the allocation will continue through normal allocation processing. Prior to allocation, SMS will call the external security manager to check the authority of the selected storage class name.
If a Storage class is selected, the data set will be controlled by SMS, so the allocation will then be passed through the Management Class ACS routine to have its Management class selected. The SMS controlled allocation is then passed to the final ACS routine to have its candidate Storage Group(s) selected.
Note: When defining a data set using JCL, the user may code new JCL parameters to specify the names of the classes, but not the name of the Storage Group.
By associating this new information with the data sets, data set management software can serve the user's needs more specifically. Having system software manage data sets is the basic goal of SMS, but SMS just provides the framework in which to accomplish data set management, not the tools to do it.
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