Fill - Populating with data

Enhanced Definition

In the context of mainframe computing, "filling" or "populating with data" refers to the process of initializing data structures, variables, files, or database tables with specific values or records. This can involve setting initial values in program memory, loading data from an input source into a target dataset or database, or presenting data on a 3270 terminal screen.

Key Characteristics

- Data Initialization: Setting program variables, arrays, or record layouts to default or specific values (e.g., SPACES, ZEROS, specific literals) at program execution start or before their first use.
- Data Loading: The bulk transfer of records from a source (e.g., a flat file, another database) into a target dataset (e.g., VSAM KSDS, sequential file) or database (e.g., DB2 table, IMS database).
- Programmatic Control: Often performed by application programs written in languages like COBOL, PL/I, or Assembler using data manipulation statements or I/O operations.
- Utility-Driven: Many high-volume data population tasks are handled by specialized z/OS utilities (e.g., IDCAMS, DB2 LOAD, IEBGENER) optimized for performance and integrity.
- Screen Presentation: In online transaction processing environments (e.g., CICS), populating fields on a 3270 terminal screen with data retrieved from backend systems for user interaction.
- Performance Criticality: The efficiency of data filling operations is crucial, especially for large datasets or databases, directly impacting batch job runtimes and online transaction response times.

Use Cases

- Initializing COBOL WORKING-STORAGE: Setting fields within a COBOL program's WORKING-STORAGE SECTION to known initial values, such as MOVE SPACES TO WS-CUSTOMER-NAME or MOVE ZEROS TO WS-TOTAL-AMOUNT.
- Loading a DB2 Table: Using the DB2 LOAD utility to efficiently populate a newly created DB2 table with millions of records from a sequential flat file, often as part of a data migration or daily batch process.
- Creating a VSAM KSDS: Populating a newly defined VSAM Key-Sequenced Data Set (KSDS) with initial records from a sorted sequential file using the IDCAMS REPRO command.
- CICS Screen Map Population: A CICS transaction retrieving customer details from a DB2 database and then populating the corresponding fields on a 3270 BMS map before sending it to the user's terminal.
- IMS Database Loading: Using the IMS DFSRRC00 utility with a DBD (Database Descriptor) and PSB (Program Specification Block) to load an IMS database with an initial set of segments from an input file.

Related Concepts

Data filling is intrinsically linked to Data Definition Language (DDL), as the structure of the data must be defined (e.g., CREATE TABLE in DB2, DEFINE CLUSTER in VSAM, DATA DIVISION in COBOL) before it can be populated. It heavily relies on JCL (Job Control Language) to invoke the programs or utilities responsible for the filling process, specifying input/output datasets and parameters. Data Manipulation Language (DML) operations, such as SQL INSERT statements or COBOL WRITE statements, are the programmatic means to perform data population. Furthermore, proper data filling is fundamental to Data Integrity, ensuring that data conforms to defined rules and constraints.

Best Practices:

Validate Input Data: Always implement robust validation routines for source data before populating target systems to prevent the introduction of corrupt, incomplete, or erroneous data.
**Lever