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Identifier

Enhanced Definition

In the context of IBM mainframe systems and z/OS, an **identifier** is a symbolic name or code assigned to a program element, data item, resource, or entity to uniquely identify and reference it within a specific scope. It serves as a label that allows programmers and the operating system to refer to specific components, variables, or system objects.

Key Characteristics

- Syntax Rules: Identifiers must adhere to specific syntax rules defined by the language (e.g., COBOL, JCL, Assembler) or system component. These rules typically dictate allowed characters (alphanumeric, sometimes special characters like @, #, $), starting character, and maximum length.
- Uniqueness: An identifier must be unique within its defined scope (e.g., a COBOL data-name within a DATA DIVISION, a JCL DDNAME within a STEP). Duplicates within the same scope will result in compilation or execution errors.
- Case Sensitivity: The sensitivity to uppercase/lowercase varies by context. JCL DDNAMEs and DSNAMEs are typically treated as uppercase, while COBOL data-names are generally case-insensitive during compilation but often written in uppercase for readability.
- Purpose: Identifiers are fundamental for referencing, addressing, and manipulating program logic, data, and system resources. They provide a human-readable way to interact with complex machine-level constructs.
- Types: Common types include data-names, procedure-names, paragraph-names (COBOL); job names, step names, DD names, dataset names (JCL); program names, transaction IDs (CICS); table names, column names (DB2).

Use Cases

- COBOL Programming: Defining data items (01 WS-RECORD-AREA PIC X(80).), paragraphs (PROCESS-INPUT-RECORD.), sections, and procedure names to structure program logic and data.
- JCL (Job Control Language): Specifying job names (//MYJOB JOB ...), step names (//STEP01 EXEC PGM=...), DDNAMEs (//SYSOUT DD SYSOUT=*), and dataset names (DSNAME=MY.PROD.FILE) to control job execution and resource allocation.
- CICS (Customer Information Control System): Naming CICS transactions (TRN1), programs (PROG1), maps (MAP1), and files (FILE1) for online transaction processing and resource management.
- DB2 for z/OS: Creating unique names for database objects such as tables (EMP_TABLE), columns (EMP_ID), indexes (EMP_PK_IDX), views, and stored procedures.
- Assembler Language: Using labels to mark instructions (LOOP: ...), defining symbolic names for data areas, and referencing system macros.

Related Concepts

Identifiers are intrinsically linked to scope, which defines the region of a program or system where an identifier is valid and unique. They are distinct from **keywords