Chapter 5 Chapter 5 The Relational Data ModelThe Relational Data Model

By Yue LuBy Yue LuCS157B Spring 2008CS157B Spring 2008Instructor: Dr.LeeInstructor: Dr.Lee

Relational Model Relational Model ConceptsConcepts

The Relational Model of Data is The Relational Model of Data is based on the concept of a based on the concept of a RelationRelation

A A RelationRelation is a is a two-dimensional two-dimensional tabletable– The columns of the table represent The columns of the table represent

attributesattributes– The rows of the table represent The rows of the table represent

entitiesentities

Relational Model Relational Model ConceptsConcepts

A A relation schemarelation schema is the name is the name and the list of attributes of a and the list of attributes of a relationrelation– Grade (studentId, assignmentId, Grade (studentId, assignmentId,

points, dateSubmitted)points, dateSubmitted) A A tupletuple is a row of a table, one is a row of a table, one

value for each attributevalue for each attribute– (101, 102, 92, 2/28/08)(101, 102, 92, 2/28/08)

Model ConceptsModel Concepts

DomainDomain DD is a set of atomic valuesis a set of atomic values– Atomic means that each value is indivisibleAtomic means that each value is indivisible

AttributeAttribute AA is the name of a role played by is the name of a role played by some domainsome domain

Relation schema Relation schema RR is the specification of a is the specification of a relation relation – Given by a name and list of attributesGiven by a name and list of attributes– Degree of a relation is the number of attributesDegree of a relation is the number of attributes

RelationRelation (instance) (instance) r(R)r(R) of a relation schemaof a relation schema– A set of n-tuples, n is degree of relation schemaA set of n-tuples, n is degree of relation schema

Characteristics of Relational Characteristics of Relational ModelModel

Relation is a set of tuplesRelation is a set of tuples– No ordering of tuplesNo ordering of tuples– No duplicate tuplesNo duplicate tuples

no two rows have all the same valuesno two rows have all the same values

Each attribute value is atomicEach attribute value is atomic– So no multiple-valued or composite So no multiple-valued or composite

attributesattributes– called called first normal formfirst normal form

Each relation is a set of assertionsEach relation is a set of assertions– Each represents a factEach represents a fact– Some facts are about relationshipsSome facts are about relationships

Representing E-R Model as Representing E-R Model as RelationsRelations

Entity class Entity class Relation schema Relation schema Entity Entity row of table row of table

– set of all entities of class set of all entities of class table table Attribute Attribute column definition column definition

(attribute)(attribute)– attribute value attribute value table element table element

Relationship type Relationship type – relation schemarelation schema– attribute(s) of relation schemaattribute(s) of relation schema

Example of Relation Schema and Example of Relation Schema and

TableTable Figure 4.2 P75Figure 4.2 P75

– Customer(Customer(accountIDaccountID,lastName,firstName, ,lastName,firstName, street, city, state, zipcode, balance)street, city, state, zipcode, balance)

accountId

lastName

firstName

street city state

zipcode

balance

101 Block Jane 1010 Main St.

Apopka

FL 30458

0.00

102 Hamilton

Cherry 3230 Dade St.

Dade City

FL 30555

4.47

103 Harrison

Kate 103 Dodd Hall

Apopka

FL 30457

30.57

104 Breaux

Carroll 76 Main St.

Apopka

FL 30458

34.58

Attributes are atomicAttributes are atomic

Composite attributes – simple attribute for each field– Customer (accountId, lastName,

firstName, street, city, state, zipcode)

Multi-valued Attributes– Represent as TablesRepresent as Tables– See Figure 4.3

Attributes are atomic Attributes are atomic (cont.)(cont.)

All other attributes values are duplicated All other attributes values are duplicated except OtherUserexcept OtherUser

The key of the schema is the setThe key of the schema is the set {accountId, {accountId, OtherUser}OtherUser}

accounaccountIDtID

lastNalastNameme

firstNafirstNameme

streetstreet citycity statestate zipcodzipcodee

OtherUOtherUserser

104104 BreauxBreaux CarrollCarroll 76 76 Main Main St.St.

ApopkaApopka FLFL 3045830458 Judy Judy BreauxBreaux

104104 BreauxBreaux CarrollCarroll 76 76 Main Main St.St.

ApopkaApopka FLFL 3045830458 Cyrus Cyrus LambeLambeauxaux

104104 BreauxBreaux CarrollCarroll 76 76 Main Main St.St.

ApopkaApopka FLFL 3045830458 Jean Jean DeauxDeaux

Representing Relationships as Representing Relationships as AttributesAttributes

One-to-manyOne-to-many– For each one-to-many relationship type RFor each one-to-many relationship type R

subject class S (one side) subject class S (one side) target class T (many side)target class T (many side)

– Add the key attributes of S to the schema of Add the key attributes of S to the schema of T T

as foreign keysas foreign keys

– Name the foreign key attributesName the foreign key attributes ues the role that S plays in relationship type Rues the role that S plays in relationship type R

– Add the attributes of the relationship type R Add the attributes of the relationship type R to schema for Tto schema for T

One-to-oneOne-to-one– choose one side and use above rulechoose one side and use above rule

Representing Relationships as Representing Relationships as TablesTables

Create a relation schema for the Create a relation schema for the relationship typerelationship type– foreign key attributes for the key of foreign key attributes for the key of

the related schemathe related schema– add attributes of the relationship add attributes of the relationship

typetype

Many-to-many Relationship Many-to-many Relationship TypesTypes

Schema: IsChildOf (child, parent) Schema: IsChildOf (child, parent) P80P80

child parent

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ReferencesReferences

Principles of Database Systems with Internet and Java Principles of Database Systems with Internet and Java Applications by Greg RiccardiApplications by Greg Riccardi

Fundamentals of Database Systems by Elmasri Fundamentals of Database Systems by Elmasri NavatheNavathe

Database Systems The Complete Book by Hector Database Systems The Complete Book by Hector Garcia-Molina, Jeffrey D.Ullman and Jennifer WidomGarcia-Molina, Jeffrey D.Ullman and Jennifer Widom