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.
- eBay alternative
The slang phrase used to describe the growing number of online marketplaces that provide selling channels that does not include eBay, the top number one ranked marketplace in terms of traffic. In a general sense of the phrase, because eBay has long been ranked as the top selling channel, all others can be called an […]
- eBay Shopping API
Also called eBay Shopping Web Services, the eBay Shopping API offers access to public read-only data such as searching for items, products, reviews, and eBay member profiles. The eBay Shopping API can be used in search tools and other buyer-focused applications.
(1) The state of a computer, usually determined by which programs are running and basic hardware and software characteristics. For example, when one speaks of running a program in a UNIX environment, it means running a program on a computer that has the UNIX operating system. One ingredient of an environment, therefore, is the operating […]
- equal error rate
(ē´kw&l er´&r rāt) (n.) Abbreviated as EER. A biometric security system predetermines the threshold values for its false acceptance rate and its false rejection rate, and when the rates are equal, the common value is referred to as the equal error rate. The value indicates that the proportion of false acceptances is equal to the […]
Abbreviated as EQ, in audio processing, equalization is the process of modifying the frequency of a sound. Equalization is most commonly used to correct signals that sound unnatural. For example, if a sound was recorded in a room that accentuates high frequencies, an equalizer can reduce those frequencies to a more normal level.