This project is a robust financial transaction processing engine developed on the IBM i (AS/400) platform. It manages account-level financial operations including deposits and withdrawals while ensuring high data integrity and a responsive user interface via green-screen subfiles.

The architecture of this system was designed to address three core challenges in enterprise financial systems: Data Integrity, Scalability, and User Efficiency.

1. Concurrency and Data Integrity (Record Locking): In a banking environment, multiple transactions might target the same account simultaneously. Using RPGLE's native record-level locking (via the UPDATE usage on the physical file), the system ensures that a record is locked the moment it is retrieved for a transaction until the update is committed. This prevents "lost updates" where one transaction overwrites another.
2. User Experience (Subfiles): To handle large volumes of data efficiently, the system uses Subfiles (SFL/SFLCTL) in the Display File. This allows the user to browse through thousands of accounts with minimal line traffic, which is a hallmark of efficient AS/400 application design.
3. Layered Architecture:
   • CLLE (Control Layer): Handles the environment setup, library lists, and error trapping at the job level.
   • DDS (Data Layer): Defines the physical structure and unique keys to enforce referential integrity at the database level.
   • RPGLE (Logic Layer): Separates business rules (like checking for sufficient funds) from the UI and database calls.

• Database Layer: The ACCOUNTS file stores the master balance, while the TRANSACT file maintains a ledger. This dual-record approach is essential for auditing.
• Transaction Logic: The RPGLE engine uses the CHAIN operation to fetch account data. If a withdrawal is requested, it subtracts from the balance only after verifying sufficient funds.
• Real-time Interface: The dashboard uses an interactive subfile. Users can select accounts using option codes (like 2 for update) which triggers the underlying logic engine.

Follow these steps to deploy and run the system on your AS/400 machine:

Create a library and the necessary source physical files to hold the code:

CRTLIB LIB(BANKINGLIB)
CRTSRCPF FILE(BANKINGLIB/QDDSSRC) RCDLEN(112)
CRTSRCPF FILE(BANKINGLIB/QRPGLESRC) RCDLEN(112)
CRTSRCPF FILE(BANKINGLIB/QCLSRC) RCDLEN(112)

Upload the files from this repository into the respective members in your new source files. Use FTP, Access Client Solutions (ACS), or VS Code with the IBM i extensions.

The objects must be compiled in the following order to resolve dependencies:

1. Physical Files (Database):

   CRTPF FILE(BANKINGLIB/ACCOUNTS) SRCFILE(BANKINGLIB/QDDSSRC)
   CRTPF FILE(BANKINGLIB/TRANSACT) SRCFILE(BANKINGLIB/QDDSSRC)

2. Display File (UI):

   CRTDSPF FILE(BANKINGLIB/ACCT_DSPF) SRCFILE(BANKINGLIB/QDDSSRC)

3. RPGLE Program (Logic):

   CRTBNDRPG PGM(BANKINGLIB/TXN_ENGINE) SRCFILE(BANKINGLIB/QRPGLESRC)

4. CLLE Program (Driver):

   CRTBNDCL PGM(BANKINGLIB/INIT_PGM) SRCFILE(BANKINGLIB/QCLSRC)

Call the initial program to set up your library list and start the dashboard:

CALL PGM(BANKINGLIB/INIT_PGM)

Developed as part of the IBM i & Data Projects Portfolio.