CICS transactions
The basic building blocks used by CICS applications are the CICS transaction, which in turn is made up of one or more units of work (UOW). Both the transaction and the UOW are typically short-lived.
A UOW is short-lived because it should not hold locks for long periods, thus causing other UOWs to wait on resources and possibly abend. A CICS transaction provides the environment in which its associated UOWs run; for example, the transaction ID, program name, and user ID. A CICS transaction is typically short-lived, because the aim is for it to use CICS resources only while it is doing work; it should not spend long periods waiting for input, for example.
Before CICS Transaction Server for OS/390® Release 3, the largest transaction processing unit that CICS understood was the terminal-related pseudoconversation. A pseudoconversational application appears to a terminal user as a continuous conversation, but consists internally of multiple transactions.