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Database Design Principles

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In this section, we will cover the fundamental principles of database design. Understanding these principles is crucial for creating efficient, scalable, and maintainable databases. This module will provide you with the knowledge to design databases that meet the needs of your applications and ensure data integrity.

Key Concepts

  1. Data Modeling

    • Entities and Attributes: Identify the main objects (entities) and their properties (attributes) that need to be stored in the database.
    • Relationships: Define how entities are related to each other (one-to-one, one-to-many, many-to-many).

  2. Normalization

    • First Normal Form (1NF): Ensure that each column contains atomic (indivisible) values and each record is unique.
    • Second Normal Form (2NF): Ensure that all non-key attributes are fully functional dependent on the primary key.
    • Third Normal Form (3NF): Ensure that all attributes are only dependent on the primary key.

  3. Primary and Foreign Keys

    • Primary Key: A unique identifier for each record in a table.
    • Foreign Key: A field in one table that uniquely identifies a row of another table, creating a relationship between the two tables.

  4. Indexes

    • Purpose: Improve the speed of data retrieval operations.
    • Types: B-tree, Hash, GiST, GIN, etc.

  5. Data Integrity

    • Entity Integrity: Ensures that each table has a primary key and that the key is unique and not null.
    • Referential Integrity: Ensures that foreign keys correctly and consistently reference primary keys in other tables.
    • Domain Integrity: Ensures that all columns in a database are in a defined domain (data type, format, range).

Practical Example

Step 1: Identify Entities and Attributes

Let's consider a simple e-commerce application. The main entities might be:

  • Customer: Attributes could include CustomerID, Name, Email, Phone.
  • Product: Attributes could include ProductID, ProductName, Price, Stock.
  • Order: Attributes could include OrderID, OrderDate, CustomerID.
  • OrderItem: Attributes could include OrderItemID, OrderID, ProductID, Quantity.

Step 2: Define Relationships

  • A Customer can place multiple Orders (one-to-many).
  • An Order can contain multiple OrderItems (one-to-many).
  • An OrderItem is associated with one Product (many-to-one).

Step 3: Create Tables with Primary and Foreign Keys

CREATE TABLE Customer (
    CustomerID SERIAL PRIMARY KEY,
    Name VARCHAR(100) NOT NULL,
    Email VARCHAR(100) UNIQUE NOT NULL,
    Phone VARCHAR(15)
);

CREATE TABLE Product (
    ProductID SERIAL PRIMARY KEY,
    ProductName VARCHAR(100) NOT NULL,
    Price DECIMAL(10, 2) NOT NULL,
    Stock INT NOT NULL
);

CREATE TABLE Order (
    OrderID SERIAL PRIMARY KEY,
    OrderDate TIMESTAMP NOT NULL,
    CustomerID INT NOT NULL,
    FOREIGN KEY (CustomerID) REFERENCES Customer(CustomerID)
);

CREATE TABLE OrderItem (
    OrderItemID SERIAL PRIMARY KEY,
    OrderID INT NOT NULL,
    ProductID INT NOT NULL,
    Quantity INT NOT NULL,
    FOREIGN KEY (OrderID) REFERENCES Order(OrderID),
    FOREIGN KEY (ProductID) REFERENCES Product(ProductID)
);

Step 4: Normalize the Database

Ensure that the database is normalized to at least 3NF:

  • 1NF: Each table has atomic columns and unique records.
  • 2NF: All non-key attributes are fully dependent on the primary key.
  • 3NF: All attributes are only dependent on the primary key.

Step 5: Create Indexes

CREATE INDEX idx_customer_email ON Customer(Email);
CREATE INDEX idx_product_name ON Product(ProductName);
CREATE INDEX idx_order_customer ON Order(CustomerID);
CREATE INDEX idx_orderitem_order ON OrderItem(OrderID);
CREATE INDEX idx_orderitem_product ON OrderItem(ProductID);

Practical Exercise

Exercise 1: Design a Library Database

Design a database for a library system with the following requirements:

  • Books: Each book has a unique identifier, title, author, and publication year.
  • Members: Each member has a unique identifier, name, and contact information.
  • Loans: Each loan records the book borrowed, the member who borrowed it, and the loan date.
  1. Identify the entities and their attributes.
  2. Define the relationships between the entities.
  3. Create the tables with primary and foreign keys.
  4. Normalize the database to 3NF.
  5. Create appropriate indexes.

Solution

  1. Entities and Attributes:

    • Book: BookID, Title, Author, PublicationYear
    • Member: MemberID, Name, ContactInfo
    • Loan: LoanID, BookID, MemberID, LoanDate

  2. Relationships:

    • A Member can borrow multiple Books (one-to-many).
    • A Book can be borrowed by multiple Members over time (many-to-many).

  3. Tables:

CREATE TABLE Book (
    BookID SERIAL PRIMARY KEY,
    Title VARCHAR(255) NOT NULL,
    Author VARCHAR(255) NOT NULL,
    PublicationYear INT
);

CREATE TABLE Member (
    MemberID SERIAL PRIMARY KEY,
    Name VARCHAR(255) NOT NULL,
    ContactInfo VARCHAR(255)
);

CREATE TABLE Loan (
    LoanID SERIAL PRIMARY KEY,
    BookID INT NOT NULL,
    MemberID INT NOT NULL,
    LoanDate TIMESTAMP NOT NULL,
    FOREIGN KEY (BookID) REFERENCES Book(BookID),
    FOREIGN KEY (MemberID) REFERENCES Member(MemberID)
);

  1. Normalization:

    • 1NF: Each table has atomic columns and unique records.
    • 2NF: All non-key attributes are fully dependent on the primary key.
    • 3NF: All attributes are only dependent on the primary key.

  2. Indexes:

CREATE INDEX idx_book_title ON Book(Title);
CREATE INDEX idx_member_name ON Member(Name);
CREATE INDEX idx_loan_book ON Loan(BookID);
CREATE INDEX idx_loan_member ON Loan(MemberID);

Conclusion

In this section, we covered the fundamental principles of database design, including data modeling, normalization, primary and foreign keys, indexes, and data integrity. By following these principles, you can create efficient, scalable, and maintainable databases. In the next section, we will delve deeper into normalization and its importance in database design.

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