Unit – II :ER Model and Relational Algebra
1. Basic Concepts of E–R (Entity-Relationship) Model The Entity–Relationship (ER) Model is a high-level data model proposed by Peter Chen in 1976 . It provides a conceptual framework to describe the structure of a database using real-world objects (entities), their characteristics (attributes), and how they interact (relationships). ER Models are mainly represented by ER Diagrams which are graphical notations. 1. Entities An Entity is an object in the real world that is distinguishable from other objects . Entities can be physical (Student, Book, Car) or conceptual (Course, Department, Salary). Types of Entities: Strong Entity Can exist independently. Has a primary key that uniquely identifies it. Example: Student (identified by Roll_No). 🔹 ER Diagram Notation: Rectangle (e.g., STUDENT ) Weak Entity Cannot exist without being related to a strong entity. Identified using a partial key (discriminator) and linked with a strong entity through an ide...