Entity-Relationship Modeling Overview

Study Notes

ER-modeling is a data modeling method in software engineering for creating conceptual data models.
Entity-Relationship Diagrams (ERDs) visually represent this modeling method.
ERDs aim to enhance database understanding, serve as documentation, and link logical database structures to users.

An entity represents a real-world object, either animate or inanimate, identifiable within a system.
Denoted as rectangles in ER diagrams.
An entity set is a collection of similar entities, e.g., a set of all students in a school.

Attributes are properties representing entities, each having specific values.
Attributes must fit within defined domains; e.g., a student's name must be alphabetic, and age cannot be negative.

Key Attribute: Uniquely identifies an entity within its set (e.g., a student’s roll number).
Composite Attribute: Composed of other attributes (e.g., student address includes pin code, state, country).
Single-valued Attribute: Contains one value (e.g., Social Security Number).
Multi-valued Attribute: Can hold multiple values (e.g., multiple phone numbers).
Derived Attribute: Values not stored directly but calculated from other attributes.

Super Key: A set of attributes uniquely identifying an entity.
Candidate Key: A minimal super key; multiple candidate keys can exist within an entity set.
Primary Key: A specific candidate key selected to uniquely identify an entity set.

Relationships denote associations between entities, represented by diamond shapes in ER diagrams.
Example relationships include "works_at" for an employee and a department or "enrolls" for a student and a course.

The degree of a relationship set signifies the number of participating entities:
- Unary (Degree 1): Exists among instances of a single entity type (e.g., one person married to one individual).
- Binary: Involves two different entity types.
- Ternary: Involves three different entity types.