Upgraded ER displaying systems Transparencies

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Section 11 Enhanced ER demonstrating strategies Transparencies © Pearson Education Limited, 2004

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Chapter 11 - Objectives The constraints of the essential ER displaying ideas and the necessities to model more unpredictable applications utilizing upgraded information demonstrating ideas. The primary ideas related with the Enhanced Entity–Relationship (EER) show called specialization/speculation. © Pearson Education Limited, 2004

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Chapter 11 - Objectives A documentation for showing specialization/speculation in an EER chart. The most effective method to make tables that speak to specialization/speculation in an EER demonstrate. © Pearson Education Limited, 2004

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The EER demonstrate Basic ideas are regularly splendidly satisfactory for the portrayal of the information necessities for various database applications. Be that as it may, fundamental ideas can restrict when demonstrating more mind boggling database applications with a lot of information or potentially information with complex interrelationships. © Pearson Education Limited, 2004

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The EER demonstrate Stimulated need to build up extra "semantic" displaying ideas. Unique ER show with extra semantic ideas is alluded to as the Enhanced Entity–Relationship (EER) demonstrate. © Pearson Education Limited, 2004

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The EER demonstrate One of the most valuable ideas related with the EER model is called specialization/speculation. © Pearson Education Limited, 2004

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Specialization/speculation Associated with unique sorts of substances known as superclasses and subclasses, and the procedure of property legacy. © Pearson Education Limited, 2004

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Superclasses and subclasses Superclass A substance that incorporates at least one unmistakable groupings of its events, which require to be spoken to in an information display. Subclass An unmistakable gathering of events of an element sort, which require to be spoken to in an information display. © Pearson Education Limited, 2004

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Superclass/subclass relationship Superclass/subclass relationship is balanced (1:1). Every individual from a subclass is likewise an individual from the superclass however has a particular part. © Pearson Education Limited, 2004

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Superclasses and subclasses We can utilize superclasses and subclasses to abstain from portraying diverse sorts of substances with perhaps extraordinary characteristics inside a solitary element. Can likewise indicate connections that are just connected with specific subclasses and not with superclass. © Pearson Education Limited, 2004

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AllStaff table holding points of interest of all staff © Pearson Education Limited, 2004

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Attribute legacy An element event in a subclass speaks to the same 'true' protest as in the superclass. Thus, an individual from a subclass acquires those properties related with the superclass, yet may likewise have subclass-particular characteristics . © Pearson Education Limited, 2004

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Specialization/speculation Specialization The way toward augmenting the contrasts between individuals from a substance by recognizing their recognizing attributes. Speculation The way toward limiting the contrasts between substances by recognizing their normal qualities. © Pearson Education Limited, 2004

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Staff substance with subclasses speaking to occupation parts © Pearson Education Limited, 2004

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Shared subclass and a subclass with its own subclass © Pearson Education Limited, 2004

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Constraints on specialization/speculation Two limitations may apply to a specialization/speculation called investment imperatives and disjoint requirements. Cooperation requirement Determines whether each event in the superclass must take part as an individual from a subclass. May be obligatory or discretionary. © Pearson Education Limited, 2004

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Vehicle element into vehicle sorts © Pearson Education Limited, 2004

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Constraints on specialization/speculation Disjoint limitation Describes the relationship between individuals from the subclasses and demonstrates whether it is feasible for an individual from a superclass to be an individual from, at least one than one, subclass. May be disjoint or nondisjoint © Pearson Education Limited, 2004

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Constraints on specialization/speculation There are four classes of imperatives of specialization and speculation: required and disjoint discretionary and disjoint obligatory and nondisjoint discretionary and nondisjoint © Pearson Education Limited, 2004

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Creating tables to speak to specialization/speculation © Pearson Education Limited, 2004

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Tables speaking to Staff and the Branch elements © Pearson Education Limited, 2004

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Tables speaking to the Vehicle substance © Pearson Education Limited, 2004

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