flowchart.md

Bank Management System - Flowchart & System Flow

Last Updated: October 31, 2025
Project: Banking Management System
Course: System Software, IIIT Bangalore

📚 Documentation Navigation

• ← Back to Main README
• Quick Start Guide - Get started in 5 minutes
• Class Diagram - UML architecture
• Workflow - Implementation logic

---

System Overview

┌─────────────────────────────────────────────────────────────┐
│                    BANK MANAGEMENT SYSTEM                    │
│                   (Client-Server Architecture)               │
└─────────────────────────────────────────────────────────────┘
                              │
                              ▼
        ┌─────────────────────────────────────────┐
        │         TCP/IP Socket (Port 8080)        │
        └─────────────────────────────────────────┘
                              │
                ┌─────────────┴─────────────┐
                │                           │
                ▼                           ▼
        ┌──────────────┐          ┌──────────────┐
        │    Server    │          │   Client(s)  │
        │  (Fork-based │          │  (Multiple)  │
        │  Concurrent) │          │              │
        └──────────────┘          └──────────────┘
                │
                ▼
        ┌──────────────┐
        │  File-based  │
        │   Database   │
        │  (w/ Locks)  │
        └──────────────┘

1. Main System Flow

START
  │
  ├─► Server Initialization
  │     ├─► Create Socket (AF_INET, SOCK_STREAM)
  │     ├─► Bind to Port 8080
  │     ├─► Listen for connections
  │     └─► Initialize Database Files
  │
  ├─► Client Connection
  │     ├─► Accept Connection
  │     ├─► Fork New Process
  │     └─► Handle Client in Child Process
  │
  ├─► User Authentication
  │     ├─► Display Login Screen
  │     ├─► Validate Credentials
  │     ├─► Check Session Status (One session per user)
  │     └─► Determine User Role
  │
  ├─► Role-Based Menu
  │     ├─► Customer Menu
  │     ├─► Employee Menu
  │     ├─► Manager Menu
  │     └─► Administrator Menu
  │
  ├─► Execute Operations
  │     ├─► File Locking (fcntl)
  │     ├─► Read/Write Data
  │     ├─► Update Records
  │     └─► Release Locks
  │
  └─► Logout & Cleanup
        ├─► Mark Session Inactive
        ├─► Close Connection
        └─► Exit Child Process

2. Authentication Flow

Client Connects → Display Login → Enter Credentials
                                         │
                                         ▼
                                  Validate User
                                         │
                    ┌────────────────────┼────────────────────┐
                    │                    │                    │
                 INVALID              VALID               INACTIVE
                    │                    │                    │
                    ▼                    ▼                    ▼
              Retry Login      Check Session Status    Account Disabled
                                         │
                    ┌────────────────────┼────────────────────┐
                    │                                         │
              SESSION_ACTIVE                           SESSION_INACTIVE
                    │                                         │
                    ▼                                         ▼
          Already Logged In                         Mark Session Active
              (Deny)                                          │
                                                              ▼
                                                    Load Role-Based Menu

3. Customer Operations

Customer Menu

1. View Account Balance
2. Deposit Money
3. Withdraw Money
4. Transfer Funds
5. Apply for Loan
6. View Loan Status
7. Change Password
8. Add Feedback
9. View Transaction History
10. Logout
11. Exit

Deposit/Withdraw Flow

Request Operation
      │
      ▼
Lock Account File (Write Lock)
      │
      ▼
Read Current Balance
      │
      ▼
Validate Operation (Sufficient funds for withdraw)
      │
      ▼
Update Balance
      │
      ▼
Create Transaction Record
      │
      ▼
Write to Files
      │
      ▼
Release Lock
      │
      ▼
Confirm to User

Fund Transfer Flow

Request Transfer (From A to B)
      │
      ▼
Lock Account A (Write Lock)
      │
      ▼
Lock Account B (Write Lock)
      │
      ▼
Validate Accounts & Balance
      │
      ▼
Deduct from Account A
      │
      ▼
Add to Account B
      │
      ▼
Create Transaction Record
      │
      ▼
Write All Changes
      │
      ▼
Release Both Locks
      │
      ▼
Confirm Success

4. Employee Operations

Employee Menu

1. Add New Customer
2. Modify Customer Details
3. View Assigned Loan Applications
4. Approve/Reject Loans
5. View Customer Transactions
6. Change Password
7. Logout
8. Exit

Add Customer Flow

Get Customer Details
      │
      ▼
Lock User File (Write Lock)
      │
      ▼
Lock Account File (Write Lock)
      │
      ▼
Create User Record
  ├─ userId (auto-increment)
  ├─ role = CUSTOMER_ROLE
  ├─ session_active = INACTIVE
  ├─ account_active = ACTIVE
  └─ Personal Details
      │
      ▼
Create Account Record
  ├─ accountId = userId
  └─ accountBalance = 0
      │
      ▼
Write Records
      │
      ▼
Release Locks
      │
      ▼
Confirm Success

Loan Processing Flow

View Assigned Loans (assignedID = employeeId)
      │
      ▼
Select Loan
      │
      ▼
Lock Loan File (Write Lock)
      │
      ▼
Choose Action: Approve/Reject
      │
      ├─► Approve
      │     ├─► Lock Account File
      │     ├─► Credit Loan Amount
      │     ├─► Update loanStatus = APPROVED
      │     └─► Release Locks
      │
      └─► Reject
            ├─► Update loanStatus = REJECTED
            └─► Release Lock

5. Manager Operations

Manager Menu

1. Activate Customer Account
2. Deactivate Customer Account
3. Assign Loan Applications to Employees
4. Review Customer Feedback
5. Change Password
6. Logout
7. Exit

Loan Assignment Flow

View Unassigned Loans (assignedID = -1)
      │
      ▼
Lock Loan File (Write Lock)
      │
      ▼
Select Loan
      │
      ▼
Enter Employee ID
      │
      ▼
Update assignedID = employeeId
      │
      ▼
Write to File
      │
      ▼
Release Lock
      │
      ▼
Confirm Assignment

Feedback Review Flow

View Non-Reviewed Feedback
      │
      ▼
Lock Feedback File (Write Lock)
      │
      ▼
Select Feedback
      │
      ▼
Add Action/Response
      │
      ▼
Update reviewStatus = REVIEWED
      │
      ▼
Write to File
      │
      ▼
Release Lock
      │
      ▼
Confirm Review

6. Administrator Operations

Administrator Menu

1. Add New Bank Employee
2. Modify Customer/Employee Details
3. Manage User Roles
4. Change Password
5. Logout
6. Exit

Add Employee Flow

Get Employee Details
      │
      ▼
Lock User File (Write Lock)
      │
      ▼
Create User Record
  ├─ userId (auto-increment)
  ├─ role = EMPLOYEE_ROLE or MANAGER_ROLE
  ├─ session_active = INACTIVE
  ├─ account_active = ACTIVE
  └─ Personal Details
      │
      ▼
Write Record
      │
      ▼
Release Lock
      │
      ▼
Confirm Success

7. File Locking Mechanism

Operation Request
      │
      ▼
Open File (O_RDWR)
      │
      ▼
Determine Lock Type
      │
      ├─► Read Operation → F_RDLCK (Shared Lock)
      └─► Write Operation → F_WRLCK (Exclusive Lock)
      │
      ▼
fcntl(fd, F_SETLKW, lock) - Blocking Wait
      │
      ▼
Lock Acquired
      │
      ▼
Perform File Operation
      │
      ▼
fcntl(fd, F_SETLK, F_UNLCK) - Release Lock
      │
      ▼
Close File

8. ACID Properties Implementation

Atomicity

• All operations within a transaction complete or none do
• Use file locking to ensure atomic updates

Consistency

• Validate all inputs before processing
• Check account balances before withdrawals
• Verify user roles before operations

Isolation

• File locks prevent concurrent modifications
• Read locks for queries, write locks for updates
• Multiple read locks allowed, exclusive write locks

Durability

• All changes written to disk immediately
• Binary file format ensures data persistence
• Transaction logs maintain operation history

9. Database Structure

Files

• user.db - User records (User struct)
• account.db - Account records (Account struct)
• loan.db - Loan records (Loan struct)
• transaction.db - Transaction records (Transaction struct)
• feedback.db - Feedback records (Feedback struct)

User Record

typedef struct {
    int userId;
    int role;                    // 1=Admin, 2=Employee, 3=Manager, 4=Customer
    int session_active;          // 1=Active, 0=Inactive
    int account_active;          // 1=Active, 0=Inactive
    char name[50];
    char age[5];
    char address[100];
    char phone[20];
    char username[20];
    char password[20];
} User;

Account Record

typedef struct {
    int accountId;
    int accountBalance;
} Account;

Loan Record

typedef struct {
    int loanId;
    int loanAmount;
    int accountID;
    int assignedID;              // -1=Not assigned, else employeeId
    int loanStatus;              // 0=Processing, 1=Approved, 2=Rejected
} Loan;

Transaction Record

typedef struct {
    int transactionId;
    int previousAmount;
    int transactionAmount;
    int lastAmount;
    int from_uid;
    int to_uid;
} Transaction;

Feedback Record

typedef struct {
    int feedbackId;
    int userId;
    char feedback[1000];
    char action[1000];
    int reviewStatus;            // 0=Not Reviewed, 1=Reviewed
} Feedback;

10. Concurrency Scenarios

Scenario 1: Multiple Readers

• Multiple customers can view balance simultaneously
• Shared read locks (F_RDLCK) allow concurrent access
• No blocking between readers

Scenario 2: Reader-Writer Conflict

• Customer A viewing balance (read lock)
• Customer B depositing money (write lock)
• Writer waits for reader to finish
• Exclusive access granted to writer

Scenario 3: Writer-Writer Conflict

• Customer A withdrawing (write lock)
• Customer B depositing (write lock)
• Second writer waits for first to complete
• Sequential execution enforced

Scenario 4: Fund Transfer (Multiple Locks)

• Lock both accounts in order
• Prevents deadlock by consistent ordering
• Atomic operation across two accounts

11. Session Management

Login Attempt
      │
      ▼
Lock User File (Read)
      │
      ▼
Check session_active
      │
      ├─► ACTIVE → Deny Login
      └─► INACTIVE → Continue
            │
            ▼
      Upgrade to Write Lock
            │
            ▼
      Set session_active = ACTIVE
            │
            ▼
      Release Lock
            │
            ▼
      Grant Access

Logout
      │
      ▼
Lock User File (Write)
      │
      ▼
Set session_active = INACTIVE
      │
      ▼
Release Lock

12. Error Handling

• File Open Error: Log error, notify client, return to menu
• Lock Timeout: Retry with timeout, notify if failed
• Insufficient Funds: Release locks, send error message
• Invalid Input: Validate, request re-entry
• User Not Found: Send error message
• Connection Lost: Cleanup resources, release locks, mark session inactive

13. Communication Protocol

Message Format

• Client-Server communication via TCP sockets
• send_message(fd, msg) - Send string message
• receive_message(fd, buffer) - Receive string message
• Blocking I/O for synchronous operations

Client-Server Interaction

Client                          Server
  │                               │
  ├──── Connect ─────────────────►│
  │                               │
  │◄──── Login Prompt ────────────┤
  │                               │
  ├──── Credentials ─────────────►│
  │                               │
  │◄──── Menu Options ────────────┤
  │                               │
  ├──── Operation Request ───────►│
  │                               │
  │◄──── Result/Confirmation ─────┤
  │                               │
  ├──── Logout ──────────────────►│
  │                               │
  │◄──── Disconnect ──────────────┤

14. System Initialization

Server Start
      │
      ▼
Check Database Files
      │
      ├─► Exist → Load Existing Data
      │
      └─► Don't Exist
            │
            ▼
      Create Database Directory
            │
            ▼
      Create Default Admin
        ├─ userId: 1
        ├─ role: ADMIN_ROLE
        ├─ username: "admin"
        └─ password: "admin123"
            │
            ▼
      Initialize Empty Files
        ├─ user.dat
        ├─ account.dat
        ├─ loan.dat
        ├─ transaction.dat
        └─ feedback.dat

15. Complete Operation Flows

Deposit Money Flow (Detailed)

Customer → Select Deposit Option
      │
      ▼
Enter Amount to Deposit
      │
      ▼
Validate Amount (> 0)
      │
      ├─► Invalid → Display Error → Return to Menu
      │
      ▼ Valid
Lock Account File (Write Lock - F_WRLCK)
      │
      ▼
Read Current Account Record
      │
      ▼
Calculate New Balance
  oldBalance = account.accountBalance
  newBalance = oldBalance + depositAmount
      │
      ▼
Update Account Record
  account.accountBalance = newBalance
      │
      ▼
Write Updated Account to File
      │
      ▼
Create Transaction Record
  transactionId = generateUniqueTransactionId()
  from_uid = -1 (indicates deposit)
  to_uid = accountId
  previousAmount = oldBalance
  transactionAmount = depositAmount
  lastAmount = newBalance
      │
      ▼
Write Transaction to File
      │
      ▼
Release Account Lock
      │
      ▼
Display Success Message
  "Deposit Successful!"
  "New Balance: ₹{newBalance}"
      │
      ▼
Return to Menu

Withdraw Money Flow (Detailed)

Customer → Select Withdraw Option
      │
      ▼
Enter Amount to Withdraw
      │
      ▼
Validate Amount (> 0)
      │
      ├─► Invalid → Display Error → Return to Menu
      │
      ▼ Valid
Lock Account File (Write Lock - F_WRLCK)
      │
      ▼
Read Current Account Record
      │
      ▼
Check Sufficient Balance
  currentBalance >= withdrawAmount ?
      │
      ├─► NO → Release Lock → Display Error → Return to Menu
      │
      ▼ YES
Calculate New Balance
  oldBalance = account.accountBalance
  newBalance = oldBalance - withdrawAmount
      │
      ▼
Update Account Record
  account.accountBalance = newBalance
      │
      ▼
Write Updated Account to File
      │
      ▼
Create Transaction Record
  transactionId = generateUniqueTransactionId()
  from_uid = accountId
  to_uid = -1 (indicates withdrawal)
  previousAmount = oldBalance
  transactionAmount = withdrawAmount
  lastAmount = newBalance
      │
      ▼
Write Transaction to File
      │
      ▼
Release Account Lock
      │
      ▼
Display Success Message
  "Withdrawal Successful!"
  "New Balance: ₹{newBalance}"
      │
      ▼
Return to Menu

Apply for Loan Flow (Detailed)

Customer → Select Apply for Loan
      │
      ▼
Enter Loan Amount
      │
      ▼
Validate Amount (> 0)
      │
      ├─► Invalid → Display Error → Return to Menu
      │
      ▼ Valid
Lock Loan File (Write Lock)
      │
      ▼
Create New Loan Record
  loanId = generateUniqueLoanId()
  loanAmount = requestedAmount
  accountID = customer.userId
  assignedID = -1 (LOAN_NOTASSIGNED)
  loanStatus = 0 (LOAN_PROCESSING)
      │
      ▼
Write Loan Record to File
      │
      ▼
Release Loan Lock
      │
      ▼
Display Success Message
  "Loan Application Submitted!"
  "Loan ID: {loanId}"
  "Status: Processing"
  "You will be notified once processed"
      │
      ▼
Return to Menu

View Transaction History Flow

Customer → Select View Transactions
      │
      ▼
Lock Transaction File (Read Lock - F_RDLCK)
      │
      ▼
Search All Transactions
  WHERE from_uid = userId OR to_uid = userId
      │
      ▼
Read Matching Records into Array
      │
      ▼
Release Transaction Lock
      │
      ▼
Display Transaction Table
  ┌──────┬──────────┬────────┬──────────┬──────────┐
  │  ID  │   Type   │ Amount │  Before  │  After   │
  ├──────┼──────────┼────────┼──────────┼──────────┤
  │ 1001 │ Deposit  │  5000  │  10000   │  15000   │
  │ 1002 │ Withdraw │  2000  │  15000   │  13000   │
  │ 1003 │ Transfer │  1000  │  13000   │  12000   │
  └──────┴──────────┴────────┴──────────┴──────────┘
      │
      ▼
Wait for User Input (Press Enter)
      │
      ▼
Return to Menu

16. Role-Based Access Control Matrix

Operation	Customer	Employee	Manager	Admin
View Own Balance	✓	✗	✗	✗
Deposit Money	✓	✗	✗	✗
Withdraw Money	✓	✗	✗	✗
Transfer Funds	✓	✗	✗	✗
Apply for Loan	✓	✗	✗	✗
View Loan Status	✓	✗	✗	✗
Submit Feedback	✓	✗	✗	✗
View Own Transactions	✓	✗	✗	✗
Add Customer	✗	✓	✗	✗
Modify Customer	✗	✓	✗	✓
Process Loans	✗	✓	✗	✗
View Customer Transactions	✗	✓	✗	✗
Assign Loans	✗	✗	✓	✗
Activate/Deactivate Account	✗	✗	✓	✗
Review Feedback	✗	✗	✓	✗
Add Employee/Manager	✗	✗	✗	✓
Change User Role	✗	✗	✗	✓
Modify Any User	✗	✗	✗	✓
Change Own Password	✓	✓	✓	✓
Logout	✓	✓	✓	✓

17. State Transition Diagrams

User Session States

┌─────────────┐
│   LOGGED    │
│     OUT     │◄──────────────┐
└─────────────┘               │
       │                      │
       │ Login Success        │ Logout
       │                      │
       ▼                      │
┌─────────────┐               │
│   LOGGED    │               │
│     IN      │───────────────┘
└─────────────┘
       │
       │ Connection Lost
       │
       ▼
┌─────────────┐
│  FORCE      │
│  LOGOUT     │
└─────────────┘

Loan Application States

┌─────────────┐
│   CREATED   │
│ (Customer)  │
└─────────────┘
       │
       │ Submit
       │
       ▼
┌─────────────┐
│ UNASSIGNED  │
│ (assignedID │
│    = -1)    │
└─────────────┘
       │
       │ Manager Assigns
       │
       ▼
┌─────────────┐
│  ASSIGNED   │
│ (assignedID │
│ = empId)    │
└─────────────┘
       │
       │ Employee Reviews
       │
       ├──────────┬──────────┐
       │          │          │
       ▼          ▼          ▼
┌──────────┐ ┌──────────┐ ┌──────────┐
│ APPROVED │ │ REJECTED │ │PROCESSING│
│(Status=1)│ │(Status=2)│ │(Status=0)│
└──────────┘ └──────────┘ └──────────┘
       │          │
       │          │
       ▼          ▼
┌──────────────────────┐
│   FINAL STATE        │
│ (No further changes) │
└──────────────────────┘

Account States

┌─────────────┐
│   CREATED   │
│  (Active)   │
└─────────────┘
       │
       │ Manager Deactivates
       │
       ▼
┌─────────────┐
│ DEACTIVATED │
│ (Inactive)  │
└─────────────┘
       │
       │ Manager Activates
       │
       ▼
┌─────────────┐
│  ACTIVATED  │
│  (Active)   │
└─────────────┘

Feedback States

┌─────────────┐
│  SUBMITTED  │
│ (Customer)  │
└─────────────┘
       │
       │ Submit
       │
       ▼
┌─────────────┐
│   PENDING   │
│ (Status=0)  │
└─────────────┘
       │
       │ Manager Reviews
       │
       ▼
┌─────────────┐
│  REVIEWED   │
│ (Status=1)  │
│ + Action    │
└─────────────┘

18. Data Flow Diagrams

Level 0 DFD (Context Diagram)

                    ┌──────────────┐
                    │              │
        ┌──────────►│   Banking    │◄──────────┐
        │           │  Management  │           │
        │           │    System    │           │
        │           │              │           │
        │           └──────────────┘           │
        │                  │                   │
        │                  │                   │
   ┌────────┐         ┌────────┐         ┌────────┐
   │Customer│         │Employee│         │Manager │
   └────────┘         └────────┘         └────────┘
        │                  │                   │
        │                  │                   │
        │           ┌──────────────┐           │
        └──────────►│              │◄──────────┘
                    │     Admin    │
                    │              │
                    └──────────────┘

Level 1 DFD (System Processes)

Customer ──────► [1.0 Authentication] ──────► User DB
                         │
                         ▼
              [2.0 Account Operations]
                    │         │
                    ▼         ▼
              Account DB  Transaction DB
                    │
                    ▼
              [3.0 Loan Management]
                    │
                    ▼
                 Loan DB
                    │
                    ▼
              [4.0 Feedback System]
                    │
                    ▼
              Feedback DB

19. Sequence Diagrams

Fund Transfer Sequence

Customer    Client    Server    Account DB    Transaction DB
   │           │         │            │              │
   │──Request──►│         │            │              │
   │           │──Send───►│            │              │
   │           │         │──Lock A────►│              │
   │           │         │◄──Locked────│              │
   │           │         │──Lock B────►│              │
   │           │         │◄──Locked────│              │
   │           │         │──Read A────►│              │
   │           │         │◄──Data──────│              │
   │           │         │──Read B────►│              │
   │           │         │◄──Data──────│              │
   │           │         │──Update A──►│              │
   │           │         │──Update B──►│              │
   │           │         │──Create Txn─┼─────────────►│
   │           │         │──Unlock────►│              │
   │           │◄─Result─│             │              │
   │◄─Display──│         │             │              │

20. Summary

This flowchart document provides comprehensive visualization of:

• System architecture and components
• User authentication and authorization flows
• Role-specific operations and menus
• Database operations with concurrency control
• File locking mechanisms
• ACID property implementation
• Error handling strategies
• Communication protocols
• State transitions
• Data flow patterns

For implementation details, refer to:

• Main README - Complete project documentation and setup
• Quick Start Guide - Get started in 5 minutes
• Class Diagram - UML architecture visualization
• Workflow - System workflow implementation
• Source Code - code/src/ and code/include/ directories

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📖 Related Documentation

Document	Description	Link
README	Main documentation, installation, usage	README.md
Quick Start	5-minute setup guide	QUICK_START.md
Class Diagram	UML architecture	class_diagram.puml
Workflow	Implementation logic	workflow.c
Source Code	Implementation files	../code/src/
Headers	Function declarations	../code/include/

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End of Flowchart Documentation