Lesson 4 Flashcards
entity-relationship (ER) model
high-level representation of data requirements, ignoring implementation details
Entity
person, place, product, concept, or activity
Relationship
statement about two entities
Attribute
descriptive property of an entity
Reflexive relationship
relates an entity to itself
ER diagram
schematic picture of entities, relationships, and attributes
Entity type
set of things
Relationship type
set of related things
Attribute type
set of values
Entity instance
Individual thing
Relationship instance
statement about entity instances
attribute instance
Individual value
Analysis for Database Design
Conceptual design
Strong entity
entity with own primary key
can exist independent of other entities
Weak entity
entity with composite key
must depend on strong entities to exist
cardinality
refers to maxima and minima of relationships and attributes
*one-to-one
*one-to-many
*many-to-many
Relationship maximum
Greatest number of instances of one entity that can relate to a single instance of another entity
one-to-many
Relationship minimum
Least number of instances of one entity that can relate to a single instance of another entity
Subtype entity
subset of another entity type, called the supertype entity
partition
A partition of a supertype entity is a group of mutually exclusive subtype entities
Database Design
After entities, relationships, attributes, cardinality, and strong and weak entities are determined, the designer looks for supertype and subtype entities.
crow’s foot notation
depicts cardinality as a circle (zero), short line (one), or three short lines (many)
Artificial Key
single column primary key created by the database designer when no suitable single column or composite primary key exist
functional dependence
dependence of one column on another
