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Unformatted text preview: is one that meets two conditions: 1. The entity is existence‐dependent, it cannot exist without the entity with which it has a relationship. 2. The entity has a primary key that is partially or totally derived from the parent entity in the relationship. For example, a company insurance policy may cover an employee and their dependents. An EMPLOYEE may or may not have any DEPENDANTS, however a DEPENDENT must be associated with an EMPLOYEE and if the EMPLOYEE is deleted then the DEPENDENT is also deleted. DEPENDENT is a weak entity in the relationship “EMPLOYEE has DEPENDENT”. Relationship Participation: Participation in a relationship is either optional or mandatory. Optional participation: means that one entity occurrence does not require a corresponding entity occurrence in the relationship. For example, an EMPLOYEE may have no DEPENDENT. Therefore the DEPENDENT entity is optional for the EMPLOYEE entity. The Crow’s Foot notation , an optional relationship is shown by drawing a small circle(O) on the side...
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This document was uploaded on 03/07/2014.
- Spring '09