1. What is Business Delegate Pattern?

Why loose coupling between tiers?

It is always recommended to develop presentation tier and business tier comps as loosely coupled comps, i.e., the degree of dependency should be less between both tiers. So the modifications done in presentation tier comps should not affect business tier comps and vice-versa.

The PM/Project Leader divides team into two parties:

• Party 1: Business tier developers - uses Java classes or Spring or Hibernate to develop business logic and persistence logic
• Party 2: Presentation tier developers - uses Servlet/JSP technologies and develops view/controller layer logics

Since these two parties can work parallelly either by staying in the same company or in two different branches of the same company, we need loose coupling between presentation tier comps and business tier comps.

2. Three Responsibilities of Business Delegate

3. Responsibility a) VO to BO Conversion

Problem (without Business Delegate)

// Problem: DTO class mirrors BO class types
public class EmployeeDTO {         // Presentation tier
    private Integer empno;
    private String ename;
    private String eaddr;
    private String salary;         // If DB changes salary to double,
    private String desg;           // this must change too!
    // setters and getters
}

public class EmployeeBO {          // Business tier
    private Integer empno;
    private String ename;
    private String eaddr;
    private Integer salary;        // Changed to double in DB
    private Integer grossSalary;   // Business tier level
    private Integer netSalary;     // Business tier level
    // setters and getters
}

Solution: Business Delegate converts VO to BO

Key insight: For any change happened in Business tier DB table, we are forced to modify other business tier comps like BO, DAO, Business Delegate (not a problem because they are in the same tier). But there is no need modifying any code in VO class, Servlet comp of presentation tier, because VO class keeps all the inputs as String values always.

4. Responsibility b) Exception Translation

Problem (without Business Delegate)

Solution: Convert to project-specific exception

// Custom project-specific exception
public class InternalProblemException extends Exception {
    public InternalProblemException(String msg) {
        super(msg);
    }
}

// In BusinessDelegate: catch technology-specific, throw project-specific
public class EmployeeOperations {
    // BusinessDelegate class

    public String registerEmployee(EmployeeVO vo) throws InternalProblemException {
        try {
            // ... business logic + DAO calls
        } catch (SQLException sqle) {
            // Catch technology-specific exception
            // Convert to project-specific user-defined exception
            throw new InternalProblemException(sqle.getMessage());
        }
    }
}

// In Servlet: catches ONLY InternalProblemException
// If DAO changes from JDBC to Hibernate, only BusinessDelegate changes.
// Servlet code stays the same.

// Controller Servlet code:
try {
    // ... business logic
    // ... invoke service method
} catch (InternalProblemException ipe) {
    // project-specific exception, not technology-specific
    ipe.printStackTrace();
}

5. Responsibility c) Transaction Management

Transaction Management (TxMgmt) deals with 3 operations:

1. Begin Tx - con.setAutoCommit(false)
2. Execute logic - execute the queries
3. Commit or Rollback Tx - con.commit() or con.rollback()

Problem: Separate connections per DAO

Solution: Single shared connection

6. Full-Length Industry Project: Employee Registration

High-Level Design (HLD)

Low-Level Design (LLD)

Project Structure

EmployeeVO.java (Presentation tier - all Strings)

package com.nbi.employee.vo;

public class EmployeeVO {
    private String empno;
    private String ename;
    private String eaddr;
    private String salary;
    private String desg;

    // All properties are String regardless of actual DB types.
    // Presentation tier never changes when DB types change.

    public String getEmpno() { return empno; }
    public void setEmpno(String empno) { this.empno = empno; }
    public String getEname() { return ename; }
    public void setEname(String ename) { this.ename = ename; }
    public String getEaddr() { return eaddr; }
    public void setEaddr(String eaddr) { this.eaddr = eaddr; }
    public String getSalary() { return salary; }
    public void setSalary(String salary) { this.salary = salary; }
    public String getDesg() { return desg; }
    public void setDesg(String desg) { this.desg = desg; }
}

HREmployeeBO.java and FinanceEmployeeBO.java

// HREmployeeBO.java
package com.nbi.employee.bo;

public class HREmployeeBO {
    private int empno;
    private String ename;
    private String eaddr;
    private double salary;

    public HREmployeeBO(int empno, String ename, String eaddr, double salary) {
        this.empno = empno;
        this.ename = ename;
        this.eaddr = eaddr;
        this.salary = salary;
    }

    public int getEmpno() { return empno; }
    public String getEname() { return ename; }
    public String getEaddr() { return eaddr; }
    public double getSalary() { return salary; }
}

// FinanceEmployeeBO.java
package com.nbi.employee.bo;

public class FinanceEmployeeBO {
    private int empno;
    private String ename;
    private String eaddr;
    private double salary;
    private double netSalary;

    public FinanceEmployeeBO(int empno, String ename, String eaddr,
                              double salary, double netSalary) {
        this.empno = empno;
        this.ename = ename;
        this.eaddr = eaddr;
        this.salary = salary;
        this.netSalary = netSalary;
    }

    public int getEmpno() { return empno; }
    public String getEname() { return ename; }
    public String getEaddr() { return eaddr; }
    public double getSalary() { return salary; }
    public double getNetSalary() { return netSalary; }
}

InternalProblemException.java

package com.nbi.employee.exception;

public class InternalProblemException extends Exception {
    public InternalProblemException(String msg) {
        super(msg);
    }
}

HREmployeeDAO.java

package com.nbi.employee.dao;

import com.nbi.employee.bo.HREmployeeBO;
import java.sql.Connection;
import java.sql.PreparedStatement;

public class HREmployeeDAO {
    private static final String INSERT_QUERY =
        "INSERT INTO HR_Employee (empno, ename, eaddr, salary) VALUES (?, ?, ?, ?)";

    private final Connection con;

    // Connection injected by BusinessDelegate (not created internally)
    public HREmployeeDAO(Connection con) {
        this.con = con;
    }

    public int insertRecord(HREmployeeBO bo) throws Exception {
        PreparedStatement ps = con.prepareStatement(INSERT_QUERY);
        ps.setInt(1, bo.getEmpno());
        ps.setString(2, bo.getEname());
        ps.setString(3, bo.getEaddr());
        ps.setDouble(4, bo.getSalary());
        return ps.executeUpdate();
    }
}

FinanceEmployeeDAO.java

package com.nbi.employee.dao;

import com.nbi.employee.bo.FinanceEmployeeBO;
import java.sql.Connection;
import java.sql.PreparedStatement;

public class FinanceEmployeeDAO {
    private static final String INSERT_QUERY =
        "INSERT INTO Finance_Employee (empno, ename, eaddr, salary, net_salary) VALUES (?, ?, ?, ?, ?)";

    private final Connection con;

    public FinanceEmployeeDAO(Connection con) {
        this.con = con;
    }

    public int insertRecord(FinanceEmployeeBO bo) throws Exception {
        PreparedStatement ps = con.prepareStatement(INSERT_QUERY);
        ps.setInt(1, bo.getEmpno());
        ps.setString(2, bo.getEname());
        ps.setString(3, bo.getEaddr());
        ps.setDouble(4, bo.getSalary());
        ps.setDouble(5, bo.getNetSalary());
        return ps.executeUpdate();
    }
}

EmployeeOperations.java (Business Delegate - all 3 responsibilities)

package com.nbi.employee.delegate;

import com.nbi.employee.bo.HREmployeeBO;
import com.nbi.employee.bo.FinanceEmployeeBO;
import com.nbi.employee.dao.HREmployeeDAO;
import com.nbi.employee.dao.FinanceEmployeeDAO;
import com.nbi.employee.exception.InternalProblemException;
import com.nbi.employee.factory.ConnectionFactory;
import com.nbi.employee.vo.EmployeeVO;
import java.sql.Connection;

public class EmployeeOperations {

    public String registerEmployee(EmployeeVO vo) throws InternalProblemException {
        Connection con = null;
        try {
            // RESPONSIBILITY a) Convert VO (all Strings) to BO (correct types)
            int empno = Integer.parseInt(vo.getEmpno());
            double salary = Double.parseDouble(vo.getSalary());
            double netSalary = salary * 0.75;  // business logic: 25% tax

            HREmployeeBO hrBO = new HREmployeeBO(
                empno, vo.getEname(), vo.getEaddr(), salary);
            FinanceEmployeeBO finBO = new FinanceEmployeeBO(
                empno, vo.getEname(), vo.getEaddr(), salary, netSalary);

            // RESPONSIBILITY c) Single connection for Transaction Management
            con = ConnectionFactory.getConnection();
            con.setAutoCommit(false);  // BEGIN TRANSACTION

            // Create both DAO classes with SHARED connection
            HREmployeeDAO hrDAO = new HREmployeeDAO(con);
            FinanceEmployeeDAO finDAO = new FinanceEmployeeDAO(con);

            // Execute both inserts
            int hrCount = hrDAO.insertRecord(hrBO);
            int finCount = finDAO.insertRecord(finBO);

            // Both succeeded: COMMIT
            con.commit();
            System.out.println("Transaction committed. HR: " + hrCount
                + ", Finance: " + finCount);
            return "Employee registration successful";

        } catch (NumberFormatException nfe) {
            return "Invalid input format: " + nfe.getMessage();

        } catch (Exception e) {
            // RESPONSIBILITY b) Convert technology-specific exception
            // to project-specific user-defined exception
            try {
                if (con != null) {
                    con.rollback();  // ROLLBACK both tables
                    System.out.println("Transaction rolled back");
                }
            } catch (Exception rollbackEx) {
                rollbackEx.printStackTrace();
            }

            // Wrap technology-specific exception (SQLException/HibernateException)
            // into project-specific InternalProblemException
            throw new InternalProblemException(
                "Employee registration failed: " + e.getMessage());

        } finally {
            ConnectionFactory.closeConnection(con);
        }
    }
}

Application.java (simulates Controller Servlet)

package com.nbi.employee;

import com.nbi.employee.delegate.EmployeeOperations;
import com.nbi.employee.exception.InternalProblemException;
import com.nbi.employee.vo.EmployeeVO;

public class Application {
    public static void main(String[] args) {
        EmployeeOperations delegate = new EmployeeOperations();

        // Scenario 1: Successful registration
        System.out.println("=== Scenario 1: Successful Registration ===");
        EmployeeVO vo1 = new EmployeeVO();
        vo1.setEmpno("1001");
        vo1.setEname("Rajesh Kumar");
        vo1.setEaddr("Hyderabad");
        vo1.setSalary("75000");
        vo1.setDesg("Senior Developer");

        try {
            String result = delegate.registerEmployee(vo1);
            System.out.println("Result: " + result);
            // forward to show_result.jsp
        } catch (InternalProblemException ipe) {
            System.out.println("Error: " + ipe.getMessage());
            // forward to error.jsp
        }

        System.out.println();

        // Scenario 2: Invalid input (VO to BO conversion fails)
        System.out.println("=== Scenario 2: Invalid Salary ===");
        EmployeeVO vo2 = new EmployeeVO();
        vo2.setEmpno("1002");
        vo2.setEname("Priya Singh");
        vo2.setEaddr("Mumbai");
        vo2.setSalary("not_a_number");  // invalid!
        vo2.setDesg("Manager");

        try {
            String result = delegate.registerEmployee(vo2);
            System.out.println("Result: " + result);
        } catch (InternalProblemException ipe) {
            System.out.println("Error: " + ipe.getMessage());
        }

        System.out.println();

        // Scenario 3: DB failure (simulated - table doesn't exist)
        System.out.println("=== Scenario 3: DB Failure ===");
        try {
            String result = delegate.registerEmployee(vo1);
            System.out.println("Result: " + result);
        } catch (InternalProblemException ipe) {
            // This is InternalProblemException, NOT SQLException
            // Controller doesn't know which DB technology is used
            System.out.println("Error (project-specific): " + ipe.getMessage());
        }
    }
}

Expected Output

Key observations from the project

7. DB Schema (from course notes)

-- HR Employee table
CREATE TABLE HR_Employee (
    empno   NUMBER(10) NOT NULL ENABLE,
    ename   VARCHAR2(20 BYTE),
    eaddr   VARCHAR2(20 BYTE),
    desg    VARCHAR2(20 BYTE),
    CONSTRAINT HR_Employee_PK PRIMARY KEY (empno)
);

-- Finance Employee table
CREATE TABLE Finance_Employee (
    empno      NUMBER(10) NOT NULL ENABLE,
    ename      VARCHAR2(20 BYTE),
    eaddr      VARCHAR2(20 BYTE),
    desg       VARCHAR2(20 BYTE),
    salary     FLOAT(126),
    CONSTRAINT Finance_Employee_PK PRIMARY KEY (empno)
);

-- Sequence for auto-generated employee IDs
CREATE SEQUENCE empno_seq MINVALUE 1 MAXVALUE 1000
    INCREMENT BY 1 START WITH 1 CACHE 20 NOORDER NOCYCLE;

8. When to Use and When NOT to Use

When to use Business Delegate

When NOT to use

9. Quick Reference Card

Business Delegate Design Pattern in Java

Complete Tutorial | 10 Sections | Full Employee Registration Project with HLD and LLD | VO to BO Conversion | Exception Translation | Transaction Management | Multiple Scenarios | 12 Interview Questions

1. What is Business Delegate Pattern?

Why loose coupling between tiers?

It is always recommended to develop presentation tier and business tier comps as loosely coupled comps, i.e., the degree of dependency should be less between both tiers. So the modifications done in presentation tier comps should not affect business tier comps and vice-versa.

The PM/Project Leader divides team into two parties:

• Party 1: Business tier developers - uses Java classes or Spring or Hibernate to develop business logic and persistence logic
• Party 2: Presentation tier developers - uses Servlet/JSP technologies and develops view/controller layer logics

Since these two parties can work parallelly either by staying in the same company or in two different branches of the same company, we need loose coupling between presentation tier comps and business tier comps.

2. Three Responsibilities of Business Delegate

3. Responsibility a) VO to BO Conversion

Problem (without Business Delegate)

// Problem: DTO class mirrors BO class types
public class EmployeeDTO {         // Presentation tier
    private Integer empno;
    private String ename;
    private String eaddr;
    private String salary;         // If DB changes salary to double,
    private String desg;           // this must change too!
    // setters and getters
}

public class EmployeeBO {          // Business tier
    private Integer empno;
    private String ename;
    private String eaddr;
    private Integer salary;        // Changed to double in DB
    private Integer grossSalary;   // Business tier level
    private Integer netSalary;     // Business tier level
    // setters and getters
}

Solution: Business Delegate converts VO to BO

Key insight: For any change happened in Business tier DB table, we are forced to modify other business tier comps like BO, DAO, Business Delegate (not a problem because they are in the same tier). But there is no need modifying any code in VO class, Servlet comp of presentation tier, because VO class keeps all the inputs as String values always.

4. Responsibility b) Exception Translation

Problem (without Business Delegate)

Solution: Convert to project-specific exception

// Custom project-specific exception
public class InternalProblemException extends Exception {
    public InternalProblemException(String msg) {
        super(msg);
    }
}

// In BusinessDelegate: catch technology-specific, throw project-specific
public class EmployeeOperations {
    // BusinessDelegate class

    public String registerEmployee(EmployeeVO vo) throws InternalProblemException {
        try {
            // ... business logic + DAO calls
        } catch (SQLException sqle) {
            // Catch technology-specific exception
            // Convert to project-specific user-defined exception
            throw new InternalProblemException(sqle.getMessage());
        }
    }
}

// In Servlet: catches ONLY InternalProblemException
// If DAO changes from JDBC to Hibernate, only BusinessDelegate changes.
// Servlet code stays the same.

// Controller Servlet code:
try {
    // ... business logic
    // ... invoke service method
} catch (InternalProblemException ipe) {
    // project-specific exception, not technology-specific
    ipe.printStackTrace();
}

5. Responsibility c) Transaction Management

Transaction Management (TxMgmt) deals with 3 operations:

1. Begin Tx - con.setAutoCommit(false)
2. Execute logic - execute the queries
3. Commit or Rollback Tx - con.commit() or con.rollback()

Problem: Separate connections per DAO

Solution: Single shared connection

6. Full-Length Industry Project: Employee Registration

High-Level Design (HLD)

Low-Level Design (LLD)

Project Structure

EmployeeVO.java (Presentation tier - all Strings)

package com.nbi.employee.vo;

public class EmployeeVO {
    private String empno;
    private String ename;
    private String eaddr;
    private String salary;
    private String desg;

    // All properties are String regardless of actual DB types.
    // Presentation tier never changes when DB types change.

    public String getEmpno() { return empno; }
    public void setEmpno(String empno) { this.empno = empno; }
    public String getEname() { return ename; }
    public void setEname(String ename) { this.ename = ename; }
    public String getEaddr() { return eaddr; }
    public void setEaddr(String eaddr) { this.eaddr = eaddr; }
    public String getSalary() { return salary; }
    public void setSalary(String salary) { this.salary = salary; }
    public String getDesg() { return desg; }
    public void setDesg(String desg) { this.desg = desg; }
}

HREmployeeBO.java and FinanceEmployeeBO.java

// HREmployeeBO.java
package com.nbi.employee.bo;

public class HREmployeeBO {
    private int empno;
    private String ename;
    private String eaddr;
    private double salary;

    public HREmployeeBO(int empno, String ename, String eaddr, double salary) {
        this.empno = empno;
        this.ename = ename;
        this.eaddr = eaddr;
        this.salary = salary;
    }

    public int getEmpno() { return empno; }
    public String getEname() { return ename; }
    public String getEaddr() { return eaddr; }
    public double getSalary() { return salary; }
}

// FinanceEmployeeBO.java
package com.nbi.employee.bo;

public class FinanceEmployeeBO {
    private int empno;
    private String ename;
    private String eaddr;
    private double salary;
    private double netSalary;

    public FinanceEmployeeBO(int empno, String ename, String eaddr,
                              double salary, double netSalary) {
        this.empno = empno;
        this.ename = ename;
        this.eaddr = eaddr;
        this.salary = salary;
        this.netSalary = netSalary;
    }

    public int getEmpno() { return empno; }
    public String getEname() { return ename; }
    public String getEaddr() { return eaddr; }
    public double getSalary() { return salary; }
    public double getNetSalary() { return netSalary; }
}

InternalProblemException.java

package com.nbi.employee.exception;

public class InternalProblemException extends Exception {
    public InternalProblemException(String msg) {
        super(msg);
    }
}

HREmployeeDAO.java

package com.nbi.employee.dao;

import com.nbi.employee.bo.HREmployeeBO;
import java.sql.Connection;
import java.sql.PreparedStatement;

public class HREmployeeDAO {
    private static final String INSERT_QUERY =
        "INSERT INTO HR_Employee (empno, ename, eaddr, salary) VALUES (?, ?, ?, ?)";

    private final Connection con;

    // Connection injected by BusinessDelegate (not created internally)
    public HREmployeeDAO(Connection con) {
        this.con = con;
    }

    public int insertRecord(HREmployeeBO bo) throws Exception {
        PreparedStatement ps = con.prepareStatement(INSERT_QUERY);
        ps.setInt(1, bo.getEmpno());
        ps.setString(2, bo.getEname());
        ps.setString(3, bo.getEaddr());
        ps.setDouble(4, bo.getSalary());
        return ps.executeUpdate();
    }
}

FinanceEmployeeDAO.java

package com.nbi.employee.dao;

import com.nbi.employee.bo.FinanceEmployeeBO;
import java.sql.Connection;
import java.sql.PreparedStatement;

public class FinanceEmployeeDAO {
    private static final String INSERT_QUERY =
        "INSERT INTO Finance_Employee (empno, ename, eaddr, salary, net_salary) VALUES (?, ?, ?, ?, ?)";

    private final Connection con;

    public FinanceEmployeeDAO(Connection con) {
        this.con = con;
    }

    public int insertRecord(FinanceEmployeeBO bo) throws Exception {
        PreparedStatement ps = con.prepareStatement(INSERT_QUERY);
        ps.setInt(1, bo.getEmpno());
        ps.setString(2, bo.getEname());
        ps.setString(3, bo.getEaddr());
        ps.setDouble(4, bo.getSalary());
        ps.setDouble(5, bo.getNetSalary());
        return ps.executeUpdate();
    }
}

EmployeeOperations.java (Business Delegate - all 3 responsibilities)

package com.nbi.employee.delegate;

import com.nbi.employee.bo.HREmployeeBO;
import com.nbi.employee.bo.FinanceEmployeeBO;
import com.nbi.employee.dao.HREmployeeDAO;
import com.nbi.employee.dao.FinanceEmployeeDAO;
import com.nbi.employee.exception.InternalProblemException;
import com.nbi.employee.factory.ConnectionFactory;
import com.nbi.employee.vo.EmployeeVO;
import java.sql.Connection;

public class EmployeeOperations {

    public String registerEmployee(EmployeeVO vo) throws InternalProblemException {
        Connection con = null;
        try {
            // RESPONSIBILITY a) Convert VO (all Strings) to BO (correct types)
            int empno = Integer.parseInt(vo.getEmpno());
            double salary = Double.parseDouble(vo.getSalary());
            double netSalary = salary * 0.75;  // business logic: 25% tax

            HREmployeeBO hrBO = new HREmployeeBO(
                empno, vo.getEname(), vo.getEaddr(), salary);
            FinanceEmployeeBO finBO = new FinanceEmployeeBO(
                empno, vo.getEname(), vo.getEaddr(), salary, netSalary);

            // RESPONSIBILITY c) Single connection for Transaction Management
            con = ConnectionFactory.getConnection();
            con.setAutoCommit(false);  // BEGIN TRANSACTION

            // Create both DAO classes with SHARED connection
            HREmployeeDAO hrDAO = new HREmployeeDAO(con);
            FinanceEmployeeDAO finDAO = new FinanceEmployeeDAO(con);

            // Execute both inserts
            int hrCount = hrDAO.insertRecord(hrBO);
            int finCount = finDAO.insertRecord(finBO);

            // Both succeeded: COMMIT
            con.commit();
            System.out.println("Transaction committed. HR: " + hrCount
                + ", Finance: " + finCount);
            return "Employee registration successful";

        } catch (NumberFormatException nfe) {
            return "Invalid input format: " + nfe.getMessage();

        } catch (Exception e) {
            // RESPONSIBILITY b) Convert technology-specific exception
            // to project-specific user-defined exception
            try {
                if (con != null) {
                    con.rollback();  // ROLLBACK both tables
                    System.out.println("Transaction rolled back");
                }
            } catch (Exception rollbackEx) {
                rollbackEx.printStackTrace();
            }

            // Wrap technology-specific exception (SQLException/HibernateException)
            // into project-specific InternalProblemException
            throw new InternalProblemException(
                "Employee registration failed: " + e.getMessage());

        } finally {
            ConnectionFactory.closeConnection(con);
        }
    }
}

Application.java (simulates Controller Servlet)

package com.nbi.employee;

import com.nbi.employee.delegate.EmployeeOperations;
import com.nbi.employee.exception.InternalProblemException;
import com.nbi.employee.vo.EmployeeVO;

public class Application {
    public static void main(String[] args) {
        EmployeeOperations delegate = new EmployeeOperations();

        // Scenario 1: Successful registration
        System.out.println("=== Scenario 1: Successful Registration ===");
        EmployeeVO vo1 = new EmployeeVO();
        vo1.setEmpno("1001");
        vo1.setEname("Rajesh Kumar");
        vo1.setEaddr("Hyderabad");
        vo1.setSalary("75000");
        vo1.setDesg("Senior Developer");

        try {
            String result = delegate.registerEmployee(vo1);
            System.out.println("Result: " + result);
            // forward to show_result.jsp
        } catch (InternalProblemException ipe) {
            System.out.println("Error: " + ipe.getMessage());
            // forward to error.jsp
        }

        System.out.println();

        // Scenario 2: Invalid input (VO to BO conversion fails)
        System.out.println("=== Scenario 2: Invalid Salary ===");
        EmployeeVO vo2 = new EmployeeVO();
        vo2.setEmpno("1002");
        vo2.setEname("Priya Singh");
        vo2.setEaddr("Mumbai");
        vo2.setSalary("not_a_number");  // invalid!
        vo2.setDesg("Manager");

        try {
            String result = delegate.registerEmployee(vo2);
            System.out.println("Result: " + result);
        } catch (InternalProblemException ipe) {
            System.out.println("Error: " + ipe.getMessage());
        }

        System.out.println();

        // Scenario 3: DB failure (simulated - table doesn't exist)
        System.out.println("=== Scenario 3: DB Failure ===");
        try {
            String result = delegate.registerEmployee(vo1);
            System.out.println("Result: " + result);
        } catch (InternalProblemException ipe) {
            // This is InternalProblemException, NOT SQLException
            // Controller doesn't know which DB technology is used
            System.out.println("Error (project-specific): " + ipe.getMessage());
        }
    }
}

Expected Output

Key observations from the project

7. DB Schema (from course notes)

-- HR Employee table
CREATE TABLE HR_Employee (
    empno   NUMBER(10) NOT NULL ENABLE,
    ename   VARCHAR2(20 BYTE),
    eaddr   VARCHAR2(20 BYTE),
    desg    VARCHAR2(20 BYTE),
    CONSTRAINT HR_Employee_PK PRIMARY KEY (empno)
);

-- Finance Employee table
CREATE TABLE Finance_Employee (
    empno      NUMBER(10) NOT NULL ENABLE,
    ename      VARCHAR2(20 BYTE),
    eaddr      VARCHAR2(20 BYTE),
    desg       VARCHAR2(20 BYTE),
    salary     FLOAT(126),
    CONSTRAINT Finance_Employee_PK PRIMARY KEY (empno)
);

-- Sequence for auto-generated employee IDs
CREATE SEQUENCE empno_seq MINVALUE 1 MAXVALUE 1000
    INCREMENT BY 1 START WITH 1 CACHE 20 NOORDER NOCYCLE;

8. When to Use and When NOT to Use

When to use Business Delegate

When NOT to use

9. Quick Reference Card