entity-relationship model (diagram)
(n.) Also called an entity-relationship (ER) diagram, 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.
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.
- Watch Datamation's editor James Maguire moderate roundtable discussions with tech experts from companies such as Accenture, Dell, Blue Jeans Network, Microsoft and more »
Does this sound familiar? An online service promises to help your small business cut costs, increase productivity, make your coffee and walk your... Read More »Who's Moving Ahead in Cloud Computing?
The future remains, well, cloudy. But either way: Amazon, look out. Microsoft is gaining fast. Read More »We Can't Give Up on Privacy!
Even new and emerging technologies that can make our lives easier, safer and healthier can jeopardize our privacy. Read More »
The trend for the past two years has been for shoppers to spend more online during the holiday season. How do you typically shop for holiday... Read More »How to Create a Desktop Shortcut to a Website
This Webopedia guide will show you how to create a desktop shortcut to a website using Firefox, Chrome or Internet Explorer (IE). Read More »Flash Data Storage Vendor Trends
Although it is almost impossible to keep up with the pace of ongoing product releases, here are three recent highlights in the flash data storage... Read More »