Lecture 3A

Lecture Overview

  • Data Modelling and Databases

Learning Objectives

  • Understand Entity Relationship and Data Modelling

Information Systems

  • Definition: Set of interrelated components that collect and process data to produce information.

  • Importance of Data Storage: Efficient and effective organization in databases requires modeling.

Data Modelling Concepts

Key Components

  • Entities: Core components representing "things" the data is about.

  • Attributes: Characteristics that define the entities.

  • Relationships: Connections and associations between entities.

Entities Explained

  • Definition: Category or group that represents tangible or intangible items (e.g., employee, product).

  • Instance: Concrete example of an entity (e.g., specific employee records).

Examples of Entities

  • People: Lecturer (Vikas Grover), Students (James, Amy, Laura, Xiaoxia)

  • Teams: e.g., Team A, Team B

  • Customers: Categories refer to buyers in a system rather than individuals.

Attributes

  • Definition: Properties of an entity that have specific values.

  • Missing Values: Attributes can have null values for specific instances.

Types of Attributes

  • Simple: Cannot be further divided (e.g., age).

  • Composite: Can be broken down into smaller components (e.g., full address into street, city).

  • Single-Valued: One value per attribute.

  • Multi-Valued: More than one value for an attribute (needs separate entity for storing).

  • Stored vs. Derived:

    • Derived: Calculated from other attribute values.

    • Stored: Original attribute value used in derivation.

Business Rules

  • Define behavior and constraints within a domain, such as relationships in a bookstore (e.g., customers purchasing many books).

Entity-Relationship Diagrams (ERD)

Purpose and Functionality

  • Purpose: Identify and represent relationships between entities in a visual format.

  • Developed by Peter Chen in 1976.

Types of Relationships

  • Cardinality:

    • One-to-One: A to B

    • One-to-Many: A to multiple Bs

    • Many-to-Many: Multiple As to multiple Bs

  • Optionality:

    • Mandatory: Entity must participate.

    • Optional: Participation not required.

ER Diagram Components

Symbols used in ER Diagrams

  • Entity: Represented by rectangles.

  • Attribute: Represented by ovals.

  • Relationship: Represented by diamonds.

    • Types of relationships indicated with symbols for mandatory and optional.

ER Diagram Examples

  • Example 1: Employee connections with Orders and Customers.

  • Example 2: Pub and Beer relationships involving drinkers.

Conventions in ER Diagrams

  • Use singular form for entity names.

  • Capitalize the first letter of entity names, lower case for attributes.

  • Avoid using spaces in names (underscore instead).

  • Positioning of entities is flexible, but avoid crossed lines for clarity.

The Importance of ERD

  • ERD serves as a foundational step in database development.

  • Each entity corresponds to a separate table in a database.