What is an Entity Relationship Diagram

Source: https://www.lucidchart.com/pages/er-diagrams

• An Entity Relationship (ER) Diagram is a type offlowchart that illustrates how “entities” such aspeople, objects or concepts relate to each otherwithin a system

• Also known as ERDs or ER Models, they use adefined set of symbols such as rectangles,diamonds, ovals and connecting lines to showentities, relationships and their attributes. Theymirror grammatical structure, with entities asnouns and relationships as verbs.

Database design

• ER diagrams are used to model and designrelational databases, in terms of logic and businessrules (in a logical data model) and in terms of thespecific technology to be implemented (in aphysical data model.)

• In software engineering, an ER diagram is often aninitial step in determining requirements for aninformation systems project. It’s also later used tomodel a particular database or databases.

The components and features of an ER diagram• ER Diagrams are composed of entities,relationships and attributes. They also depictcardinality, which defines relationships in terms ofnumbers.

A definable thing—such as a person, object,concept or event—that can have data storedabout it. Think of entities as nouns. Examples:a customer, student, car or product. Typicallyshown as a rectangle.

Entity type: A group of definable things, such as students or athletes, whereas theentity would be the specific student or athlete. Other examples: customers, cars orproducts.Entity set: Same as an entity type, but defined at a particular point in time, such asstudents enrolled in a class on the first day. Other examples: Customers whopurchased last month, cars currently registered in Florida. A related term is instance,in which the specific person or car would be an instance of the entity set.Entity categories: Entities are categorized as strong, weak or associative. A strongentity can be defined only by its own attributes, while a weak entity cannot. Anassociative entity associates entities (or elements) within an entity set.

Attribute

• A property or characteristic of an entity. Often shown as an oval or circle.

More about attribute types can be found on: https://www.lucidchart.com/pages/er-diagrams

Cardinality

• Defines the numerical attributes of the relationshipbetween two entities or entity sets. The three maincardinal relationships are one-to-one, one-to-many,and many-many. A one-to-one example would be onestudent associated with one mailing address. A one-to-many example (or many-to-one, depending on therelationship direction): One student registers formultiple courses, but all those courses have a single lineback to that one student. Many-to-many example:Students as a group are associated with multiple facultymembers, and faculty members in turn are associatedwith multiple students.

How to model data using ARIS?

DATA MODEL

TUTORIAL

• https://s3-eu-west-1.amazonaws.com/arisexpress/media/videos/ARIS-Express/en/aris_express_model_data.mp4

Other ERD tool…

• You can usehttps://www.lucidchart.com/pages/tour/ER_diagram_tool

DBMS ER Diagram examples

Clothes store

University DBMS

Manufacturing company