Data Mgmt Lab_Part_3

Data Mgmt Lab_Part_3 - Introduction to Database Design 7...

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Introduction to Database Design 7 Participation constraint - a participation constraint determines whether relation- ships must involve certain entities. An example is if every department entity has a manager entity. Participation constraints can either be total or partial. A total participation constraint says that every department has a manager. A partial participation constraint says that every employee does not have to be a manager. Overlap constraint - within an ISA hierarchy, an overlap constraint determines whether or not two subclasses can contain the same entity. Covering constraint - within an ISA hierarchy, a covering constraint determines where the entities in the subclasses collectively include all entities in the superclass. For example, with an Employees entity set with subclasses HourlyEmployee and SalaryEmployee, does every Employee entity necessarily have to be within either HourlyEmployee or SalaryEmployee? Weak entity set - an entity that cannot be identi±ed uniquely without considering some primary key attributes of another identifying owner entity. An example is including Dependent information for employees for insurance purposes. Aggregation
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Data Mgmt Lab_Part_3 - Introduction to Database Design 7...

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