BFOR-205 (Intro to Database Systems) Exam 1 Flashcards

Entity

Noun (object, person, place, thing, or concept) of which data is being maintained for in the system

Attribute

Individual characteristic(s) within an entity

Entity Strengths

• Strong Entity

• Weak Entity

• Associative Entity

Strong Entity

• Can exist independently

• Contains unique identifier (underlined)

• Drawn with single line

Weak Entity

• Cannot exist on its own; dependent on strong entity

• Partial identifier; does NOT have unique identifier

• Drawn with double lines

Associative/Bridge Entity

Resolves a many-to-many relationship by turning it into multiple one-to-many relationships, by combining primary keys (composite)

Entity Type

Collection of similar entities that share the same attributes

Entity Instance

Single occurrence of entity type

Generalization

• Bottom-up

• Defines a more general entity type (supertype) from set of specialized entities

Specialization

• Top-down

• Defines one or more specialized entities (subtypes) based on supertype

Primary Key

Unique identifier for each record of an entity

• No duplicates (ex. StudentID can only belong to one person)

• Cannot be NULL

Foreign Key

Points to primary key in another table to establish a relationship

• Can have duplicates (ex. one customer can have multiple orders)

• Can be NULL

Partial Identifier

Identifies weak entity WHEN combined with primary key of the owner strong entity

• represented with double underline

Types of Cardinalities

• Mandatory One

  • ||—————||

• Mandatory Many

  • >|—————|<

• Optional One

  • |o————o|

• Optional Many

  • >o————o<

Completeness Constraint

Determines whether supertype must also be member of at least one subtype

Disjointness Constraint

Determines whether supertype may simultaneously be a member of multiple subtypes