PB

4.1

Entity Relationship Model Overview

  • Represents high-level data requirements ignoring implementation details.

  • Guides implementation in a specific database system.

Key Objects in ER Model

  • Entity: A distinct object in the model.

  • Relationship: Represents how entities relate to each other.

  • Attribute: Information that describes an entity.

  • Reflexive Relationship: A relationship where an entity is related to itself.

Glossary and Data Dictionary

  • Glossary: Contains terms and definitions used in the model.

  • Data Dictionary: A repository of metadata that documents additional details related to entity attributes.

Detailed Description of ER Model

  • An Entity Relationship Model (ERM) is fully described using:

    • ERD (Entity Relationship Diagram): Visual representation of the model.

    • Glossary: Definitions of entity types, relationship types, and attribute types.

Components of ER Model

  • Entity Type: Set of similar entities (e.g., Students).

  • Relationship Type: Set of associations between entities (e.g., Enrolls).

  • Attribute Type: Set of values that attribute can take (e.g., Name, Age).

Instances

  • Entity Instance: A single, unique element of an entity type (e.g., John Doe).

  • Relationship Instance: A specific association between entity instances (e.g., John Doe enrolls in Course).

  • Attribute Instance: A specific value for an attribute (e.g., Age = 20).

Phases of Entity Relationship Modeling

  1. Conceptual Design:

    • Develops an entity relationship model that captures data requirements while ignoring implementation details.

  2. Logical Design:

    • Converts the ER model into tables, columns, and keys for a specific database system.

  3. Physical Design:

    • Adds indexes and specifies how tables are organized on storage media.