What is an ERD. Define the RED related terms, including entities, attributes, cardinalities and relationships

 

 Learn Computer Science(2021)

An Entity-Relationship Diagram (ERD) is a visual representation of the data model of a system, depicting the entities and their relationships to each other. ERDs are commonly used in software engineering to describe the data requirements and relationships between different entities in a system.

Component

Entities are objects or concepts within a system that have data attributes associated with them. In an ERD, entities are represented by rectangles with their names written inside. For example, in a school database, entities may include students, teachers, and classes.

Attributes are characteristics or properties of an entity. They describe the data that can be associated with an entity. In an ERD, attributes are represented by ovals connected to the entity. For example, attributes of a student entity may include student ID, name, and date of birth.

Cardinalities describe the number of instances of one entity that can be related to another entity. In an ERD, cardinalities are represented by symbols on the relationship line between entities. Common cardinalities include one-to-one (1:1), one-to-many (1:N), and many-to-many (M:N). For example, a student entity may have a one-to-many relationship with a class entity, meaning that one student can be enrolled in many classes, but each class is associated with only one student.

Relationships describe the association between two or more entities. In an ERD, relationships are represented by lines connecting the entities. Relationships can be further described using cardinalities and constraints such as mandatory or optional. For example, a student entity may have a relationship with a teacher entity, where each student is assigned to one teacher, but each teacher can have many students.

References:

Chen, P. P. (1976). The Entity-Relationship Model—toward a Unified View of Data. ACM Transactions on Database Systems (TODS), 1(1), 9–36. https://doi.org/10.1145/320434.320440

Entity relationship diagram ( ERD ): Explained ER model in DBMS (2021) Learn Computer Science. Available at: https://www.learncomputerscienceonline.com/entity-relationship-diagram/ (Accessed: March 9, 2023).