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450--ER

Database: entity relationship

E-R model Entity-relationship; model showing objects and their relationships
entity object that exists and differentiable from other objects
Concrete entity person or book
abstract entity holiday or disease
entity set set of entities of same type, can not be disjoint
attributes represents an entity, name, SSN, Phone-Num for “customer” entity.
domain of attribute permitted values
function maps entity set into a domain
Rectangles entity sets
Ellipses attributes
Diamonds relationship sets
lines links everything
one to one one A to one B, can be zero, is married to
one to many one A to many B, is mother of
many to one many A to one B, was born in
many to many many A to many B, no constratints/arrow, is class mate of
arrow points to one
participation constraints BOLD LINE, does not allow partial participation
super Key one or more attribute which which UNIQUELY identifies an entity in the entity set, can contain other attribute
candidate key a super key of subset of one
primary key candidate key that can be used to choose identities in an entity set, EX-VIN#, underlined
strong entity entity that has a primary key
weak entity entity that has no primary key
identifying owner entity whose primary key is being used
Created by: fqaium
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