Quiz 2 - Ch 5 Flashcards
Result of adding more semantic constructs to the original entity relationship (ER) model: E….. E….. R….. M…..
Extended Entity Relationship Model
Generic entity type related to one or more entity subtypes: E…. S……
Entity Supertype
Contains unique characteristics of each entity subtype: E….. S……
Entity subtype
Entity Supertypes and Subtypes: There must be d……, i………kinds of the e…. in the user’s environment
different/ identifiable/ entity
Entity Supertypes and Subtypes: The different kinds of instances should each have one or more a……. that are u…… to that kind of instance
attribute / unique
Entity supertypes and subtypes are organized in a s…………….. h…………
specialization hierarchy
S………….. h………….. depicts arrangement of higher-level entity supertypes and lower-level entity subtypes
specialization hierarchy
Relationships are described in terms of “ i….” relationships
“is-a”
S……… exists within the context of a s………
Subtype / supertype
Every s………. has one s……….. to which it is directly related
Subtype / supertype
S……….. can have many s…….
Supertype/ subtype
Specialaization Hierarchy provides the means to:
- Support a……….. i…………
- Define a special s……… a……… known as the s……….. d……..
- Define d…../o… constrains and c……/p…….. constrains
Support attribute inheritance
Define a special supertype attribute known as the subtype discriminator
Define disjoint/overlapping constraints and complete/partial constraints
Enables an entity subtype to inherit attributes and relationships of the supertype: I………….
Inheritance
All entity subtypes i………their primary key attribute from their supertype
inherite
At the implementation level, supertype and its subtype(s) maintain a …. relationship
1:1
Entity subtypes i……. a… relationships in which supertype entity participates
inherit all
Lower-level s……… i……….. all attributes and relationships from its upper-level s……….
subtypes inherit / supertype
Attribute in the supertype entity that determines to which entity subtype the supertype occurrence is related : S…………. D………..
Subtype Discriminator
Contain a unique subset of the supertype entity set : D………… S………….
Disjoint subtypes
Known as nonoverlapping subtypes: D………. s……….
disjoint subtypes
Contain nonunique subsets of the supertype entity set : O………. s…………
Overlapping subtypes
Implementation is based on the value of the subtype discriminator attribute in the supertype: D………. s……….
Disjoint subtype
Implementation requires the use of one discriminator attribute for each subtype : O………… s……………
Overlapping subtypes
Specifies whether each supertype occurrence must also be a member of at least one subtype: C………….. C………..
Completeness Constraint
P………. c……..: Not every supertype occurrence is a member of a subtype
Partial Completeness
T……….. c………..: Every supertype occurrence must be a member of at least one subtype.
Total completeness
Subtype discriminator can be null for p…… c……….
partial completeness
Top-down process : S……….
Specialization
Identifies lower-level, more specific entity subtypes from a higher-level entity supertype: S………..
Specialization
Based on grouping unique characteristics and relationships of the subtypes S………….
Specialization
Bottom-up process: G………..
Generalization
Identifies a higher-level, more generic entity supertype from lower-level entity subtypes: G……..
Generalization
Based on grouping common characteristics and relationships of the subtypes: G………….
Generalization
Virtual entity type used to represent multiple entities and relationships in ERD: E……….. C…………
Entity Cluster
Avoid the display of attributes (no key attributes) to eliminate complications that result when the inheritance rules change : E……….. C…………
Entity Cluster
Real-world identifier used to uniquely identify real-world objects: N…….. k……….
natural keys or natural identifier
Desirable Primary Key Characteristics Non I................ No c.........over time Preferably s........- a....... Preferably n.......... S.........-c...........
Non Intelligent No change over time Preferably single- attribute Preferably numeric Security-compliant
The PK should not have embedded semantic meaning other than to uniquely identify each entity instance: Non I…………
Non intelligent
The selected primary key must not be composed of any attribute that might be considerd a security risk or violation: S………… c………..
security compliance
Each primary key combination is allowed once in (…:..) relationship
M:N
Primary key used to simplify the identification of entity instances : S………… K…………..
Surrogate Keys
Surrogate Keys are useful when:
There is no n………. k………..
Selected candidate key has embedded s………. contents or is too l………
There is no natural key
Selected candidate key has embedded semantic contents or is too long
Require ensuring that the candidate key of entity in question performs properly: S………. K…..
Surrogate Keys
Use unique index and not null constraints : s……….. K………
Surrogate Keys
Data whose values change over time and for which a history of the data changes must be retained: t…….-V………….. D……….
Time-variant data
Time-variant data Requires creating a new entity in a ( .. : ..) relationship with the original entity
1:M
Occurs when a relationship is improperly or incompletely identified: D……….. t……….
Design trap
Represented in a way not consistent with the real world : D……… t………….
Design trap
Occurs when one entity is in two 1:M relationships to other entities: F………. t…………
Fan trap
Produces an association among other entities not expressed in the model: F………. t…………
Fan trap
Occur when there are multiple relationship paths between related entities: R…………. R………….
Redundant Relationships
The relationship could be safely deleted with out losing any information generation capabilities in the model: : R…………. R………….
Redundant Relationships
