Indicate

Enhanced Definition

In mainframe computing, to **indicate** refers to the act or mechanism of signaling a specific status, condition, or outcome of a process, operation, or data element. This signaling is typically achieved through predefined codes, flags, variables, or messages that programs and systems can interpret to determine subsequent actions or report results. It provides a programmatic way to convey information about the state or result of an action.

Key Characteristics

- Contextual Significance: The meaning of an indication is highly dependent on the subsystem, programming language, or component from which it originates (e.g., a COBOL switch, a JCL condition code, a DB2 SQLCODE).
- Programmatic Interpretation: Indications are designed to be programmatically checked and acted upon, enabling conditional logic, error handling, and flow control within applications and system processes.
- Standardized Values: Often, specific numeric or alphanumeric values are assigned to represent particular states (e.g., SQLCODE = 0 for success, RC=0 for successful JCL step, S0C4 for a program check abend).
- Error and Exception Handling: A primary use is to signal errors, warnings, or exceptional conditions, allowing for graceful recovery, logging, or controlled termination.
- Status Reporting: Used to convey the current state of a resource, transaction, or job step (e.g., CICS EIBRESP indicating a successful or failed API call, IMS status codes).

Use Cases

- COBOL Program Flow Control: Using 88-level condition-names or SWITCH indicators (e.g., SWITCH-1) to indicate a specific business condition (e.g., END-OF-FILE-REACHED, VALID-TRANSACTION) to control PERFORM loops or conditional logic.
- JCL Job Step Execution: The COND parameter in JCL uses return codes from previous steps to indicate their success or failure, determining whether a subsequent step should execute or be bypassed.
- DB2 SQL Operation Results: An SQLCODE or SQLSTATE variable indicates the success, warning, or error status of a SELECT, INSERT, UPDATE, or DELETE statement, and indicator variables signal NULL values.
- CICS Transaction Processing: The EIBRESP and EIBRESP2 fields in the EXEC CICS interface indicate the outcome of a CICS command, such as a file read, a program link, or a queue operation.
- IMS Database Calls: DL/I status codes in the PCB mask indicate the result of a database call, such as GE (segment not found), GA (end of segment occurrence), or II (insert successful).

Related Concepts

Indications are fundamental to error handling, program control flow, and system monitoring across the mainframe ecosystem. They are closely tied to return codes, status codes, condition codes, flags, and switches, which are the specific mechanisms used to convey these signals. Effective use of indications is crucial for building robust batch jobs, online transactions, and database applications that can adapt to varying conditions, recover from failures, and provide meaningful diagnostic information.

Best Practices:

Always Check Indications: Programs should consistently check relevant return codes, status codes, or flags after operations that can fail or have variable outcomes, especially I/O operations and external calls.
Document Indication Meanings: Clearly document the meaning of custom flags, switches, or application-specific return codes within application code comments and design specifications.
Use Standardized Error Handling: Implement consistent error handling routines that interpret indications and take appropriate actions, such as logging messages, retrying operations, or terminating gracefully.