ENTITY RELATIONSHIP DIAGRAM

The ER diagram representation is an excellent context for the introduction of the complexity of database design. There isn't always a single ER diagram for an entity. Usually, the evaluation of the goodness of an ER design requires an understanding of the enterprise being modeled and the applications to be run.

ER Diagram is a type of flowchart that illustrates how entities(people, objects, etc). ER Diagrams are most often used to design or debug relational databases in the fields of software engineering, business information systems, education, and research. They use a set of symbols such as rectangles, diamonds, ovals, and lines to depict the connection between entities and their attributes. These diagrams also are often used in conjunction with DFD, which map out the flow of information for processes or systems.

The components of an ER diagram:

Entity

A definable thing is an entity such as a person, object, concept or event that can have data stored about it.

Ex: Customer, student, car, or product. Typically represented as a rectangle.

Entities are categorized as strong, weak, or associative.

A strong entity can be defined solely by its own attributes.
A weak entity cannot be defined solely by its own attributes.
An associative entity associates entities (or elements) within an entity set.

Relationship:

How entities act upon each other or are associated with each other. For example, for course registration, the two entities would be the student and the course, and the relationship depicted is the act of enrolling, connecting the two entities in that way. Relationships are typically shown as diamonds.