ERD Diagrams

Owned by Computer Science Department
Aug 02, 2023
2 min read

An Entity-Relationship Diagram (ERD) is a type of diagram used in database design and system analysis to visually represent the logical structure of a database. It serves as a blueprint of the database and assists in designing, understanding, and communicating the data and rules of a system. ERDs are commonly used in the fields of software engineering, business information system design, and database management.

 

Key elements of an ERD include:

  1. Entity: Entities are the main objects or concepts about which information is to be collected and stored. For example, in a university database, the entities could be students, courses, and instructors.

  2. Attributes: Attributes are the properties or characteristics of entities. For example, a student entity might have attributes such as student ID, name, major, and age.

  3. Relationship: A relationship is the association that describes the interaction between entities. For example, in a university database, students 'enroll in' courses, which illustrates the relationship between the student and course entities.

  4. Cardinality: Cardinality defines the numerical attributes of the relationship between two entities or the number of occurrences in one entity which are linked to the number of occurrences in another. It can be one-to-one, one-to-many, or many-to-many.

ERDs can be categorized into three types based on the level of abstraction:

  1. Conceptual ERD: This is the highest level ERD and provides a macro view of an informational system. It focuses on the high-level system scope, the relationships between the major entities, and the business processes the system should support.

  2. Logical ERD: This diagram is a detailed view of the system, describing how the system will be implemented by the database designers. It includes all entities, relationships, attributes, primary keys and foreign keys.

  3. Physical ERD: This ERD further refines the logical ERD and describes how the system will be physically implemented in the database. It includes all tables, columns, data types, constraints, etc.

ERDs can be drawn in different notations like Chen's notation, Crow's foot notation, and the IDEF1X notation, with each having its own visual style and strengths.