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The specifies whether each entity supertype occurrence must also be a member of at least one subtype

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The completeness constraint specifies whether each entity supertype occurrence must also be a member of at least one subtype. b. The completeness constraint specifies whether each entity subtype occurrence must also be a member of at least one supertype. c. Partial completeness constraint means that every supertype occurrence is a member of a subtype. d. Total completeness constraint means that every subtype occurrence must be a member of at least one supertype.

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Thiru DBMS

Completeness Constraint

The completeness constraint specifies whether each entity supertype occurrence must also be a member of at least one subtype. The completeness constraint can be partial or total.

Partial completeness (symbolized by a circle over a single line) means that not every supertype occurrence is a member of a subtype; that is, there may be some supertype occurrences that are not members of any subtype.

A single horizontal line under the circle represents a partial completeness constraint. For example consider the following figure

The specifies whether each entity supertype occurrence must also be a member of at least one subtype

Total completeness (symbolized by a circle over a double line) means that every supertype occurrence must be a member of at least one subtype.

A double horizontal line under the circle represents a total completeness constraint. Consider the following diagram.

The specifies whether each entity supertype occurrence must also be a member of at least one subtype
 

Given the disjoint/overlapping subtypes and completeness constraints, it’s possible to have the specialization hierarchy constraint scenarios shown in the following Table

The specifies whether each entity supertype occurrence must also be a member of at least one subtype

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Entity supertype and Subtype

Specialization Hierarchy

Subtype Discriminator

Surrogate Primary key

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Extended entity relationship diagram

result of adding more semantic constructs to the ER model. This model is used to make an EER diagram

contain unique subset of supertype entity set.

subtypes that contain nonunique subsets of the supertype entity set

Specifies whether each entity supertype occurrence must also be a member of at least one subtype

(circle over single line) means that not every supertype occurrence is a member of a subtype

(circle over double line) every supertype occurrence must be a member of at least one subtype

top-down process of identifying lower-level, more specific entity subtypes from a higher-level entity supertype

bottom-up process of identifying a higher-level more generic entity supertype from lower-level entity subtypes

a virtual entity type used to represent multiple entities and relationships in the ERD

Natural key (natural identifier)

real world identifier that uniquely identifies a real world object

Primary key created by the database designer to simplify the identification of entity instances

  1. The ____ constraint specifies whether each entity supertype occurrence must also be a member of at least one subtype.

    1.   specialization
    2.   uniqueness
    3.   inheritance
    4.   completeness

  2. In addition to the normal behavior, the EER model also supports specialization ____ where a subtype can have multiple parents (supertypes).

    1.   nets
    2.   networks
    3.   lattices
    4.   webs

  3. ____ relationships occur when there are multiple relationship paths between related entities.

    1.   Shared
    2.   Redundant
    3.   Joined
    4.   Nonkey

  4. A specialization hierarchy reflects the ____ relationship between EMPLOYEE and its subtypes.

  5. A(n) ____ trap occurs when a relationship is improperly or incompletely identified and, therefore, is represented in a way that is not consistent with the real world.

    1.   entity
    2.   relationship
    3.   key
    4.   design

  6. In modeling terms, the ____ contains the common characteristics and the entity subtypes contain the unique characteristics of each entity subtype.

    1.   entity supertype
    2.   superentity
    3.   base entity
    4.   higher entity

  7. The property of ____ enables an entity subtype to inherit the attributes and relationships of the supertype.

    1.   specialization
    2.   generalization
    3.   inheritance
    4.   uniqueness

  8. The implementation of disjoint subtypes is based on the value of the subtype discriminator attribute in the ____.

    1.   supertype
    2.   subtype
    3.   primary key attribute
    4.   foreign key attribute

  9. The ____'s function is to guarantee entity integrity.

    1.   entity name
    2.   discriminator
    3.   index
    4.   primary key

  10. What is the best data type for a primary key?

    1.   numeric
    2.   text
    3.   boolean
    4.   date

  11. ____ data refer to data whose values change over time and for which you must keep a history of the data changes.

    1.   Closed
    2.   Historical
    3.   Time-complete
    4.   Time-variant

  12. Arguably, the most important characteristic of an entity is its ____.

    1.   name
    2.   primary key
    3.   relationships
    4.   attributes

  13. ____ subtypes are subtypes that contain nonunique subsets of the supertype entity set.

    1.   Shared
    2.   Overlapping
    3.   Joined
    4.   Complex

  14. One important inheritance characteristic is that all entity subtypes inherit their ____ from their supertype.

    1.   indexes
    2.   foreign keys
    3.   candidate keys
    4.   primary key attribute

  15. ____ is the bottom-up process of identifying a higher-level, more generic entity supertype from lower-level entity subtypes.

    1.   Discrimination
    2.   Specialization
    3.   Completeness
    4.   Generalization

  16. As part of database naming conventions, attribute names should use suffixes such as _ID, _NUM, or _CODE for the ____ attribute.

    1.   primary key
    2.   foreign key
    3.   index
    4.   determinant

  17. The EER model builds on ER concepts and adds support for entity supertypes, subtypes, and entity ____.

    1.   clustering
    2.   housing
    3.   joining
    4.   extension

  18. A(n) ____ is the attribute in the supertype entity that determines to which entity subtype each supertype occurrence is related.

    1.   inheritance key
    2.   subtype discriminator
    3.   supertype selector
    4.   subtype entity

  19. ____________ is used when an entity is composed of (or is formed by) a collection of other entities, but the entities are independent of each other. That is, the relationship can be classified as a ‘has_a’ relationship type.

    1.   Specialization
    2.   Generalization
    3.   Aggregation
    4.   Composition

  20. __________ is used when when two entities are associated in an aggregation association with a strong identifying relationship and deleting the parent deletes the children instances.

    1.   Specialization
    2.   Generalization
    3.   Clustering
    4.   Composition

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