Data Object

Enhanced Definition

In the mainframe context, a **data object** refers to a discrete, identifiable unit of information that is stored, processed, or manipulated by programs and systems. This can range from a single field within a record to an entire record, a segment in a hierarchical database, a row in a relational database table, or even a complete dataset or file, depending on the level of abstraction. Its primary purpose is to represent and encapsulate meaningful business or system data.

Key Characteristics

- Structured Representation: Data objects are typically defined by a specific structure (e.g., COBOL PIC clauses, DB2 CREATE TABLE statements, IMS DBD definitions) that dictates their format, length, and content.
- Persistence: Often stored persistently on direct access storage devices (DASD) or magnetic tape, allowing for retrieval and processing across different job executions or system restarts.
- Addressability: Each data object, or its components, can be uniquely identified and addressed by programs for read, write, or update operations.
- Granularity: Can exist at various levels of granularity, from elementary data items (fields) to complex composite structures (records, segments, rows, arrays).
- Type-Specific Operations: The type of a data object (e.g., numeric, alphanumeric, packed decimal) determines the valid operations that can be performed on it by programming languages like COBOL.

Use Cases

- COBOL Program Processing: A COBOL program reads a record (a data object) from an input sequential file, processes its fields (smaller data objects), and writes an updated record to an output file.
- DB2 Application Query: A CICS transaction or batch job executes an SQL SELECT statement to retrieve rows (data objects) from a DB2 table, where each row consists of multiple columns (smaller data objects).
- IMS Database Interaction: An IMS application program accesses segments (data objects) within an IMS database, navigating the hierarchical structure to retrieve related information using DL/I calls.
- JCL Parameter Passing: A PARM parameter in a JCL EXEC statement passes a small string (a data object) to a program as input, influencing its execution logic.

Related Concepts

Data objects are fundamental building blocks for datasets, files, records, and fields. They are the actual units of information that COBOL programs define using DATA DIVISION structures, and that JCL manipulates through DD statements. In database systems like DB2 and IMS, data objects manifest as rows/columns and segments respectively, managed by the DBMS and accessed via specific APIs or SQL. They are intrinsically linked to access methods (like VSAM, QSAM) which dictate how these objects are stored and retrieved efficiently.

Best Practices:

Standardized Definitions: Use COPYBOOKs in COBOL or DDL scripts in DB2 to ensure consistent and standardized definitions of data objects across all programs and systems, promoting reusability and reducing errors.
Data Validation: Implement robust data validation routines to ensure the integrity and correctness of data objects before they are stored or processed, preventing data corruption.
Efficient Access: Design data structures and choose appropriate access methods (e.g., VSAM KSDS for keyed access, DB2 indexes) to optimize the retrieval and update performance of data objects.
Data Security: Apply appropriate security measures (e.g., RACF profiles, DB2 GRANT statements) to control access to sensitive data objects, adhering to compliance requirements.