There are several ways in which a data set created by a server differs from a data set created by an ordinary SYSOUT DD or dynamic allocation.

1. Data sets created by a server use the DALRTCTK dynamic allocation text unit, which causes JES to create a unique Client Token(CTOKEN) associated with the data set from that point on.
2. The server can use the Extended Status or SYSOUT Application Programming Interface (SAPI) Subsystem Interface (SSI) calls to access a data set, specifying a CTOKEN in the selection criteria in order to request a particular data set, without needing to know any other information about the data set.
3. When a data set has a CTOKEN, JES informs the application, through the use of ENF signal 58, of events relating to the data set. Among these events are selection by a writer, deselection by a writer, and data set purge. JES also issues signals for important events related to any job that has created at least one data set with a CTOKEN, such as job purge.