CREATE TABLE Persons (
    PersonID INT IDENTITY PRIMARY KEY,
    Name VARCHAR(64),
    Username VARCHAR(64),
    Password VARCHAR(128),
    Email VARCHAR(128)
);

CREATE TABLE Engineer (
    EngineerID INT IDENTITY PRIMARY KEY,
    PersonID INT,
    FOREIGN KEY (PersonID) REFERENCES Persons(PersonID)
);

CREATE TABLE Clients (
    ClientID INT IDENTITY PRIMARY KEY,
    PersonID INT,
    EngineerID INT,
    FOREIGN KEY (PersonID) REFERENCES Persons(PersonID),
    FOREIGN KEY (EngineerID) REFERENCES Engineer(EngineerID)
);