5.28 What is a weak entity? How do weak entities relate to ID-dependent entities

Question

5.28 What is a weak entity? How do weak entities relate to ID-dependent entities?
5.30 Define subtypeandsupertype. Give an example of a subtype–supertype relationship
(other than one presented in this chapter).
5.31 Explain the difference between exclusive subtypes and inclusive subtypes. Give an
example of each.
5.32 What is a discriminator?
5.33 Explain the difference between IS-Aand HAS-Arelationships.
5.39 Describe two tests for determining if an entity is a strong entity.
5.42 How can you assess minimum cardinality for the entities in the form in Figure 5-17?
5.44 Name three patterns that use ID-dependent relationships.
5.45 Explain how the association pattern differs from the N:M strong entity pattern. What
characteristic of the report in Figure 5-21indicates that an association pattern is needed?
5.53 What entity type should come to mind when you see the words “For use by” in a form?

Explanation / Answer

Dear.. 5.28) Weak Entity: • A weak entity is an entity that cannot exist in the database without the existence on another entity • For example, an employee’s dependents cannot exist in a database without the employee existing in the database A weak entity that includes the identifier of the related strong entity, An ID-Dependent weak entity is a weak entity that must include the identifier of its parent entity as part of its composite primary key. 5.30) Subtype and Supertype Supertype is equivalent to generalization and subtype to specialization. Supertype contains all attributes in common of all specializations. A subtype entity is a special case of a supertype entity: – STUDENT : UNDERGRADUATE or GRADUATE • The supertype contains all common attributes, while the subtypes contain specific attributes. • The supertype may have a discriminator attribute that indicates the subtype. 5.31) difference between exclusive subtypes and inclusive subtypes. If subtypes are exclusive, one supertype relates to at most one subtype. If subtypes are inclusive, one supertype can relate to one or more subtypes. 5.44) Types of patterns that are use in ID-dependent relationships. The Association Pattern The Multivalued Attribute Pattern The Archtype/Instance Pattern Note: Dear.. Please post onepost per one question. This is our Cramster's one of the terms and conditions.

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