Destination

Enhanced Definition

In the context of IBM z/OS and mainframe systems, a destination refers to the specific target or location where output, messages, or data are directed after processing. It defines *where* information or results are sent, whether to a physical device, a logical queue, a data set, or another system component.

Key Characteristics

- Variety of Targets: Destinations can include physical printers, magnetic tape drives, disk data sets, JES (Job Entry Subsystem) SYSOUT queues, CICS terminals, IMS logical terminals, or even other connected systems.
- Specification Methods: Destinations are typically specified through JCL parameters (e.g., DEST on a DD statement), program code (e.g., WRITE statements in COBOL to a DD name), or system commands.
- Subsystem Management: Major subsystems like JES, CICS, and IMS play a crucial role in managing and routing output to their respective destinations, often involving queues and routing tables.
- Logical vs. Physical: A destination can be a logical entity (like a SYSOUT class or a CICS TERMINAL ID) that is then mapped by the system to a physical device or resource.
- Security and Access Control: Access to specific destinations can be controlled by security products like RACF, ensuring that only authorized users or jobs can send output to or retrieve output from sensitive targets.

Use Cases

- Batch Job Output: Directing a batch job's SYSOUT (system output) to a specific SYSOUT class for printing, archiving, or viewing via SDSF.
- CICS Transaction Messaging: Sending a message from a CICS application to a particular TERMINAL ID for display to an operator or end-user.
- IMS Transaction Routing: Routing an IMS transaction to a specific processing region or logical terminal for execution and response delivery.
- Report Generation: Specifying an output DD statement in JCL to direct a COBOL program's generated report to a sequential data set on disk.
- System Console Messages: Routing system-generated messages or alerts to a specific operator console or a system log data set.

Related Concepts

The concept of a destination is fundamental to how z/OS manages I/O and inter-component communication. It is intrinsically linked with JES for batch output management, where SYSOUT classes and DEST parameters define where job output goes. DD statements in JCL explicitly define destinations for program I/O, linking logical file names to physical resources. In online transaction processing, CICS uses destinations (terminal IDs) to route messages to specific user screens, while IMS utilizes logical terminals and transaction codes to direct messages and transactions within its hierarchical structure.

Best Practices:

Standardize SYSOUT Classes: Establish and adhere to a clear set of SYSOUT classes with well-defined purposes (e.g., A for production print, X for archive, Z for discard) to simplify output management.
Secure Sensitive Destinations: Implement robust security profiles (e.g., using RACF) to control access to destinations that handle sensitive data, ensuring only authorized entities can write to or read from them.
Monitor Spool Usage: Regularly monitor JES spool space for SYSOUT destinations to prevent overflow, which can lead to job failures and system instability.
Use Symbolic Parameters: Employ JCL symbolic parameters for common or frequently changing destinations to improve maintainability and consistency across jobs.
Implement Error Handling: Design applications and JCL to gracefully handle scenarios where a specified destination might be unavailable (e.g., a printer offline), potentially by rerouting output or logging the issue for operator intervention.