Quiz 2 - Ch 4 Flashcards
Entity Relationship Model forms the basis of an e….. r…… d……
Entity relationship diagram
E…… represents conceptual database as viewed by end user.
ERD
ERD depicts the database’s main components: E……., A……, R…….
Entities, attributes, relationships
Refers to entity set and not to single entity occurrence: E……
Entities
Corresponds to table and not to row in relational environment: E……
Entities
In both Chen and Crow’s Foot models, entity is represented by r…….. containing entity’s name
Rectangle
Entity name, a noun, is usually written in c……… l…….
capital letters
Characteristics of entities: A……….
Attributes
R………… a…………. : Must have a value, cannot be left empty
Required attribute
O……….. a………….. : Does not require a value, can be left empty
Optional attribute: Does not require a value, can be left empty
Attributes have a d………
domain
D………… is attribute’s set of possible values
domain
Attributes may s…… a domain
share
Primary key composed of more than one attribute: C…… k……..
composite key
An attribute that can be further subdivided to yield additional attributes : C……… a………
Composite Attribute
An attribute that can be further subdivided to yield additional attributes: S……… a……..
Simple Attribute
Single-value attribute can have only a s…….. v……..
Single value
A single-valued attribute is not necessarily a s…… a…….
simple attribute
M…………… a………… can have many values
Multivalued attributes
Attribute whose value may be calculated (derived) from other attributes: d…….. a……….
Derived Attributes
Need not be physically stored within database: d………. a………..
Derived Attributes
Can be derived by using an algorithm: d………. a……….
Derived Attributes
Advantages of Storing Derived Attributes
Saves CPU p……….cycle
D…… value is r…….available
Can be used to keep track oh h…….. d……..
Saves CPU processing cycle
Data value is readly available
Can be used to keep track oh historical data
Disadvantages of Storing Derived Attributes
Requires constant m…….. ensure d………value is c………, especially if any values used in the c…… change
Requires constant maintenance to ensure derived value is current, especially if any values used in the calculation change
Advantages of Non-stored Derived Attributes
Saves s……….. s……,
C…… always yields c…… v………
Saves storage space,
Computation always yields current value
Disadvantages of Non-stored Derived Attributes
Uses CPU p……….. c………
Adds coding c……..to q…….
Uses CPU processing cycles
Adds coding complexity to queries
Association between entities: R…….
Relationships
Association between entities that always operate in both directions: R……
Relationships
Entities that participate in a relationship: P……..
Participants
Describes the relationship classification (1:1,1:M): C…..
Connectivity
Expresses the minimum and maximum number of entity occurrences associated with one occurrence of related entity: C………
Cardinality
Entity exists in the database only when it is associated with another related entity occurrence: E….. D…..
Existence dependence
Entity exists apart from all of its related entities
Referred to as a strong entity or regular entity: E….. I………
Existence independence
Primary key of the related entity does not contain a primary key component of the parent entity : W…….. R……
Weak Relationship (non-identifying)
Primary key of the related entity contains a primary key component of the parent entity: S……. R……
Strong Relationships (identifying)
Weak entity meets two conditions:
E……..-d…………( Cannot exist without entity with which it has a relationship)
Has p…….. k…… that is partially or totally derived from p……e……..in relationship
Existence-dependent ( Cannot exist without entity with which it has a relationship)
Has primary key that is partially or totally derived from parent entity in relationship
One entity occurrence does not require a corresponding entity occurrence in a particular relationship: O……….. P………
Optional Participation
One entity occurrence requires a corresponding entity occurrence in a particular relationship: M…….. P……….
Mandatory participation
Indicates the number of entities or participants associated with a relationship: R………. D………
Relationship Degree
Association is maintained within a single entity
: U………… R……….
Unary Relationship
Two entities are associated: B…….. R……..
Binary Relationship
Three entities are associated: T………. R……….
Ternary Relationship
Also known as composite or bridge entities: A……….. E…………
Associative Entities
Used to represent an M:N relationship between two or more entities : A……….. E…………
Associative Entities
Is in a 1:M relationship with the parent entities: A……….. E…………
Associative Entities
Composed of the primary key attributes of each parent entity: A……….. E…………
Associative Entities
