Mainframe batch system
A COBOL batch reconciliation system that validates synthetic banking movements, updates VSAM balances, and produces deterministic rejection, audit, and summary outputs.
Architecture, COBOL development, JCL, testing, and documentation
2026
Validated on IBM Z Xplore
COBOL · JCL · VSAM KSDS · ICETOOL / DFSORT
A financial batch must reject malformed or inconsistent input before balances change, apply valid movements only once, and leave enough evidence to explain every decision. The challenge was to make those guarantees explicit across records, return codes, persisted state, and reruns.
I designed the fixed-width contracts and return-code policy, implemented the validation, reconciliation, and reporting programs in COBOL, orchestrated the flow with JCL and ICETOOL, prepared VSAM and GDG storage, and documented reproducible local and z/OS verification.
A staged daily job detects duplicate transaction identifiers, validates header-detail-trailer integrity, reconciles accepted entries against a VSAM account file, and writes separate audit, rejection, and summary outputs. Batch and transaction identifiers make reruns safe instead of silently applying a movement twice.
Each stage has a narrow responsibility and a visible return-code contract, so business rejections do not become technical failures.
ICETOOL prepares input and identifies repeated transaction IDs
Validates structure, dates, currency, and control totals
Applies account rules and updates VSAM balances
Produces summary, rejection, and audit records
The repository separates reproducible source and tests from sanitized execution evidence, and states clearly which optional capabilities were not deployed.