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Dependent

Enhanced Definition

In the context of IBM mainframe systems, a "dependent" entity is one whose successful execution, completion, or availability relies directly on the prior successful completion, specific state, or existence of another entity. This concept is fundamental to ensuring the correct sequential and logical flow of batch processing, application execution, and data integrity within the z/OS environment.

Key Characteristics

- Conditional Execution: Dependencies often dictate whether a job, job step, or program can proceed, frequently based on the return codes or completion status of preceding tasks.
- Resource Availability: A dependent process may require specific data sets, databases (e.g., DB2, IMS), or system resources to be available and in a particular state before it can begin.
- Explicit or Implicit: Dependencies can be explicitly defined (e.g., through JCL parameters, workload scheduler rules) or implicitly understood within application logic or operational procedures.
- Hierarchical Structure: Complex batch streams or application architectures often involve chains of dependencies, forming a hierarchical or directed acyclic graph (DAG) structure.
- Impact on Reliability: Unmet dependencies are a common cause of job failures, abends, and data inconsistencies if not properly managed.

Use Cases

- Batch Job Sequencing: A daily report generation job is dependent on the successful completion of an overnight data update job, ensuring the report uses the latest information.
- JCL Step Dependencies: Using the COND parameter in JCL to prevent a subsequent job step from executing if a prior step abended or returned a high condition code.
```
jcl
//STEP1 EXEC PGM=UPDATEPGM
//STEP2 EXEC PGM=REPORTPGM,COND=(0,LT,STEP1)
```
- Workload Automation: Defining predecessor-successor relationships in a job scheduler (e.g., IBM Z Workload Scheduler, CA-7, Control-M) where Job B is dependent on Job A completing with a specific status.
- Program Module Linkage: A COBOL main program is dependent on the availability and correct linkage of its called subroutines or copybook members during compilation and execution.
- Data Set Dependencies: A utility program that sorts a file is dependent on an upstream program having successfully created and populated that input file.

Related Concepts

Dependencies are central to Workload Automation and Job Scheduling systems (like IBM Z Workload Scheduler, CA-7, Control-M), which manage the complex sequencing of batch jobs. They are often expressed in JCL through parameters like COND or DD statements pointing to specific data sets. Understanding dependencies is critical for System Reliability and Data Integrity, as