ID - Identifier

Enhanced Definition

In the mainframe context, an **Identifier (ID)** is a unique name or label assigned to a resource, entity, user, program, or data component to distinguish it from others and enable its reference, access, and management within the z/OS environment. It serves as a primary means of identification for various system objects and security principals.

Key Characteristics

- Uniqueness: IDs are typically unique within their defined scope (e.g., a USERID is unique across the system, a Dataset Name (DSN) is unique within its catalog structure).
- Naming Conventions: Often subject to strict naming conventions, including character sets (alphanumeric, national characters like #, @, $), length limits (e.g., 8 characters for USERID, 44 for DSN), and hierarchical structures.
- Purpose-Driven: The structure and content of an ID often convey information about the object it identifies, such as ownership, type, or environment (e.g., PROD.APPL.DATASET.FILE for a production application dataset).
- Case Sensitivity: While some mainframe components (like UNIX System Services paths) are case-sensitive, many traditional z/OS components (e.g., USERIDs, JOBNAMEs, DSNs) often treat identifiers as uppercase or convert them to uppercase internally.
- Security Principal: User IDs are fundamental security principals, representing an individual or group, and are used by external security managers (ESMs) like RACF to control access to resources.

Use Cases

- User Authentication and Authorization: A USERID is used to log onto z/OS, TSO, CICS, or IMS, and is the primary identifier for security managers (RACF, ACF2, Top Secret) to determine access rights to datasets, programs, and other resources.
- Dataset Naming: A Dataset Name (DSN) is a hierarchical identifier (e.g., HLQ.MIDLVL.LLQ) that uniquely identifies a dataset on disk or tape, allowing programs and JCL to allocate and access it.
- Job and Step Identification: JOBNAME in JCL identifies a batch job, and STEPNAME identifies individual steps within a job, crucial for monitoring, logging, and restartability.
- Program and Module Reference: PGM names are used in JCL EXEC statements to specify the load module to be executed, and module names are used in CALL statements within COBOL or assembler programs.
- CICS Resource Definition: CICS uses various IDs, such as TRANID (transaction ID), PROGID (program ID), FILEID (file ID), and TERMID (terminal ID), to