Automatic Transaction Initiation (ATI) Feature

Enhanced Definition

Automatic Transaction Initiation (ATI) is a core CICS (Customer Information Control System) feature that allows a transaction to be started automatically without explicit user input from a terminal. It enables CICS to initiate a new task based on predefined events, such as a timer expiration, a message arriving on a queue, or an explicit `EXEC CICS START` command issued by another program.

Key Characteristics

- Event-Driven: ATI transactions are triggered by specific events rather than direct terminal input, facilitating background or scheduled processing within the CICS region.
- Asynchronous Processing: The initiated transaction runs as a separate CICS task, independent of the task that triggered it, allowing for parallel or deferred execution and improving online responsiveness.
- EXEC CICS START Command: The primary programmatic mechanism to initiate an ATI transaction, often specifying a TRANID, TERMID (even a dummy one), INTERVAL or TIME for delayed execution, and optionally FROM data to pass to the new task.
- Transient Data Queues (TDQs): A common trigger for ATI, where writing a record to an intrapartition TDQ can automatically initiate a CICS transaction associated with that TDQ if the TDQ is defined with ATI(YES) and a TRANID.
- Interval Control Program: CICS's internal component responsible for managing and dispatching START requests based on specified time intervals or absolute times, ensuring timely execution of ATI tasks.
- Resource Allocation: ATI transactions can specify a TERMID (even a dummy one) to acquire resources typically associated with terminal-initiated tasks, or run as non-terminal tasks, impacting resource usage and security context.

Use Cases

- Scheduled Batch-like Processing: Running CICS programs at specific times (e.g., end-of-day reports, nightly data synchronization, database cleanups) without requiring manual operator intervention.
- Asynchronous Message Processing: Initiating a CICS transaction to process messages arriving on an IBM MQ queue (via the CICS-MQ bridge) or records written to a Transient Data Queue, decoupling message reception from processing.
- Long-Running Background Tasks: Offloading computationally intensive or time-consuming operations from online user transactions to run in the background, improving interactive response times.
- Inter-System Communication (ISC/MRO): Used in conjunction with CICS Intersystem Communication (ISC) or Multi-Region Operation (MRO) to trigger transactions in another CICS region, facilitating distributed processing.
- Error Recovery and Retries: Automatically restarting failed transactions after a delay or triggering a recovery process based on an error condition, enhancing application resilience.

Related Concepts

ATI is a fundamental feature of CICS and is tightly integrated with its Interval Control Program, which manages the scheduling and dispatching of START requests. It frequently leverages Transient Data Queues (TDQs), where a TDQ can be defined with an ATI(YES) attribute and an associated `