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We say that an entity that is a member of a subclass inherits all the attributes of the entity as a member if superclass. ER modeling allows you to examine information specifications systematically to produce a properly-designed database. Entity-Connection product is based on the idea of true-planet organizations as well as the relationship between them. Inserting an entity in a super class implies that the entity in mandatorily inserted in all predicate-defined (or attribute defined) subclasses for which the entity satisfies the defining predicate. superclass, it should posses values for its specific attributes as well as values of its attributes as a member of the superclass. Er Diagram Optional Attribute Entity Relationship is really a higher-levels conceptual info model diagram.Deleting an entity from a super class implies that it is automatically deleted form all the subclasses to which it belongs.Example, SalariedEmployee, Hourly Employee, Manager, Secretary, Engineer, Technician. Sometimes, entities underneath an entity type can be classified to specific entities which have its own characteristics. Example, Employee represents all entities of employees. In general a super class that was identified through the generalization process usually is total, because the super class is derived from the subclasses and hence contains only the entities that are in the subclass.Ĭertain insertion and deletion rules apply to specialization and generalization as a consequence of the constraints specified earlier. Subclasses, Superclasses, and Inheritance In ER diagram, an entity type represents all entities underneath it. Hence we have the following four possible constraints on specialization Notice: that disjoint ness and completeness constraints are independent.