Input - Data entering
In the context of IBM mainframe systems and z/OS, "input" refers to any data or commands supplied to a program, application, or the operating system for processing. This data serves as the raw material for computations, transactions, updates, or system control, enabling the system to perform its intended functions. Its primary purpose is to provide the necessary information for a task to be executed.
Key Characteristics
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- Diverse Sources: Input can originate from various sources including sequential datasets, VSAM files, DB2 tables, IMS databases, CICS terminals, network connections (e.g., TN3270), or even in-stream data via JCL
SYSINDD statements. - EBCDIC Predominance: While ASCII input is possible, most native mainframe applications and data are processed in EBCDIC (Extended Binary Coded Decimal Interchange Code).
- Structured Formats: Input data is often highly structured, defined by
COPYBOOKs in COBOL or PL/I, or by database schemas, facilitating precise parsing and processing. - Batch vs. Online: Input is handled differently in batch processing (e.g., reading entire files via JCL) compared to online transaction processing (e.g., real-time user entries via CICS screens or IMS message queues).
- Access Methods: Data is accessed via specific z/OS access methods such as QSAM (Queued Sequential Access Method), VSAM (Virtual Storage Access Method), or database-specific APIs (e.g., SQL for DB2, DL/I for IMS).
- Buffering and Blocking: To optimize I/O performance, input data is typically read in blocks and buffered in memory before being processed record by record.
- Diverse Sources: Input can originate from various sources including sequential datasets, VSAM files, DB2 tables, IMS databases, CICS terminals, network connections (e.g., TN3270), or even in-stream data via JCL
Use Cases
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- Batch Job Processing: A COBOL batch program reads a sequential input file containing daily transactions (e.g., sales orders) to update a master inventory file.
- Online Transaction Entry: A CICS application receives user input from a 3270 terminal screen to process a customer inquiry, update an account, or book a flight reservation.
- Database Updates: An IMS or DB2 application receives input from a message queue or another program to insert new records, modify existing ones, or delete obsolete data.
- System Commands: A system operator enters commands via the z/OS console (e.g.,
START,STOP,MODIFY) to control the execution of system tasks or applications. - Utility Program Parameters: Input parameters are provided to z/OS utility programs (e.g., IDCAMS, IEBGENER) via
SYSINto define specific operations like dataset allocation or copying.
Related Concepts
Input is a foundational concept intrinsically linked to JCL (which defines input datasets and their characteristics), COBOL and other programming languages (which contain logic to read and process input), CICS and IMS (which manage online input from terminals or message queues), and DB2/IMS DB (which store and retrieve input data). It forms the initial phase of the classic Input-Process-Output (IPO) model, directly preceding the processing stage and influencing the resulting output. Proper input management is critical for data integrity and application functionality.
- Robust Data Validation: Implement comprehensive data validation routines as early as possible in the processing chain to ensure input data is accurate, complete, and conforms to business rules, preventing errors downstream.
- Clear Data Definitions: Use
COPYBOOKs in COBOL or DCLGEN for DB2 to standardize input data layouts, ensuring consistency across programs and reducing data mapping errors. - Efficient I/O Handling: Select appropriate access methods and optimize block sizes for input datasets to minimize physical I/O operations and improve program performance.
- Graceful Error Handling: Design programs to gracefully handle invalid input, end-of-file conditions, and I/O errors, logging issues and preventing program abends.
- Secure Input Sources: Implement security measures (e.g., RACF profiles, CICS transaction security) to restrict access to input files, terminals, and network ports to authorized users and applications.
- Audit Trails: For critical applications, maintain audit trails or logs of input transactions to support debugging, recovery, and compliance requirements.