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University of California, Davis

Application Development Methodology

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Development Technique Concepts

Entity

A fundamental thing of relevance to the enterprise, about which the enterprise needs to keep information.

Entity and Entity Type

Most businesses have suppliers, deal with products, and sell them to customers. There are thus likely to be data about individual suppliers (e.g., Poly Leisure Products of Hong Kong). Poly Leisure Products is an entity; the collection of all suppliers is the SUPPLIER entity type. The collection of all customers is the CUSTOMER entity type. A sample customer entity may be Harrods Department Store. Similarly, there is a PRODUCT entity type.

Entities that are Tangible Objects

Following are examples of entities that are tangible objects:

* ORDER, of which one entity might be a request on 6 November for 50 footballs from Poly Leisure Products

* VEHICLE, with an entity Ford Model T, Registration Number 135 AXU

* ROOM, with entities kitchen at 14 Conway Road, boardroom at James Martin & Co.

Entities that are Activities or Events of Interest to the Business

Following are examples of entities that are activities or events:

* LECTURE ATTENDANCE (e.g., John Davis attends the lecture on Entity Relationship Modeling on 3 May 1997)

* EQUIPMENT MALFUNCTION (e.g., the lighting dimmer in lecture room 2 fails at 3 PM. on 4 June 1995)

Entities that are Intangible

Following are examples of entities that are intangible:

* GEOGRAPHICAL SALES AREA (e.g., Europe, Asia, Australia)

* MARKET SECTOR (e.g., consumer, electronics, instrumentation)

* CUSTOMER TYPE (e.g., distributor, retail store)

* BUSINESS ROLE (e.g., principal, guarantor, legal advisor, broker)