Database Design: ER Model Chapter 3

Database Design Process

• The database design process consists of two main activities: database design and applications design
• Database design focuses on designing the conceptual schema for a database application
• Applications design focuses on the programs and interfaces that access the database, which is part of software engineering

Entity-Relationship (ER) Model

• The ER model is a conceptual representation of data
• It has three main concepts: entities, attributes, and relationships
• Entities are objects with existence and can be described with attributes
• Attributes can be simple, composite, or multivalued

Entities and Attributes

• Entities can be categorized into entity types and entity sets
• Entity types are categories of entities, and entity sets are collections of entities

Relationships and Relationship Types

• A relationship is an association between two or more entities with a specific meaning
• Relationships can be grouped into relationship types
• Relationship types have a degree, which is the number of participating entity types
• Examples of relationships include WORKS_ON and MANAGES

Relationship Instances and Relationship Sets

• A relationship instance is a specific instance of a relationship type
• A relationship set is the current set of relationship instances in the database
• A relationship set represents the current state of a relationship type

ER Diagrams

• ER diagrams are used to represent the ER model
• Relationship types are represented by diamond-shaped boxes
• Participating entity types are connected to the relationship type via lines

COMPANY Database Schema

• The COMPANY database schema includes entities such as DEPARTMENT, PROJECT, and EMPLOYEE
• Relationships between entities include WORKS_FOR, MANAGES, WORKS_ON, CONTROLS, SUPERVISION, and DEPENDENTS_OF