entity-relationship diagram (model)
An entity relationship model, also called an entity-relationship (ER) diagram, is a graphical representation of entities and their relationships to each other, typically used in computing in regard to the organization of data within databases or information systems. An entity is a piece of data-an object or concept about which data is stored.
Relationships Between Entities
A relationship is how the data is shared between entities. There are three types of relationships between entities:
One instance of an entity (A) is associated with one other instance of another entity (B). For example, in a database of employees, each employee name (A) is associated with only one social security number (B).
One instance of an entity (A) is associated with zero, one or many instances of another entity (B), but for one instance of entity B there is only one instance of entity A. For example, for a company with all employees working in one building, the building name (A) is associated with many different employees (B), but those employees all share the same singular association with entity A.
One instance of an entity (A) is associated with one, zero or many instances of another entity (B), and one instance of entity B is associated with one, zero or many instances of entity A. For example, for a company in which all of its employees work on multiple projects, each instance of an employee (A) is associated with many instances of a project (B), and at the same time, each instance of a project (B) has multiple employees (A) associated with it.
ER Diagram Symbols
In an ER diagram, symbols are commonly used to to represent the types of information. Most diagrams will use the following:
- Boxes represent entities.
- Diamonds represent relationships
- Circles (ovals) represent attributes.
Stay up to date on the latest developments in Internet terminology with a free newsletter from Webopedia. Join to subscribe now.
From A3 to ZZZ we list 1,559 text message and online chat abbreviations to help you translate and understand today's texting lingo. Includes Top... Read More »Huge List of Computer Certifications
Have you heard about a computer certification program but can't figure out if it's right for you? Use this handy list to help you decide. Read More »
Computer architecture provides an introduction to system design basics for most computer science students. Read More »Network Fundamentals Study Guide
Networking fundamentals teaches the building blocks of modern network design. Learn different types of networks, concepts, architecture and... Read More »The Five Generations of Computers
Learn about each of the five generations of computers and major technology developments that have led to the computing devices that we use... Read More »