Job Library

JCL Library

Enhanced Definition

While the term `Joblib` primarily refers to a Python library for parallel computing, in the context of IBM z/OS, a **Job Library** (often synonymous with a JCL Library or PROCLIB) is a partitioned data set (PDS) or partitioned data set extended (PDSE) specifically used to store JCL (Job Control Language) members. These members contain the instructions necessary for the z/OS operating system to execute batch jobs or start system tasks.

Key Characteristics

- Data Set Type: A job library is typically a PDS or PDSE, allowing it to contain multiple members, each representing a distinct JCL script or procedure.
- Member Organization: Each JCL program or routine is stored as a separate member within the library, identified by a unique 1-8 character member name.
- Execution Source: JCL members from job libraries are submitted to the Job Entry Subsystem (JES) for execution, either directly by users or applications, or invoked as started tasks or procedures.
- Concatenation: Multiple job libraries can be concatenated in a STEPLIB or JOBLIB DD statement, or in the JES PROCLIB concatenation, enabling the system to search for JCL procedures across several data sets.
- Content: Members consist of JCL statements (e.g., JOB, EXEC, DD) that define job steps, allocate resources, and specify program execution.

Use Cases

- Batch Job Submission: Storing the JCL for routine batch processing jobs, such as daily financial reconciliations, weekly report generations, or monthly database maintenance tasks.
- Procedure Libraries (PROCLIBs): Housing commonly used JCL procedures (PROCs) that can be invoked by other JCL jobs using the EXEC PROC=procname statement, promoting reusability.
- Application Deployment: Consolidating all JCL required for a specific application or system component into a dedicated job library for easier management, deployment, and version control.
- System Started Tasks: Containing the JCL for system-level started tasks (STCs) that run continuously or are initiated by the system, such as CICS regions, DB2 subsystems, or network daemons.

Related Concepts

Job libraries are fundamental to JCL (Job Control Language), serving as the primary repository for JCL members. They are processed by JES (Job Entry Subsystem), which reads the JCL from these libraries to schedule and execute jobs. They often contain JCL Procedures (PROCs), which are reusable blocks of JCL. Their content can be managed and edited using ISPF (Interactive System Productivity Facility) and are frequently controlled by Source Code Management (SCM) systems like IBM z/OS Change Management (Endevor) for versioning and change tracking.