CSE 4701 Chapter 9-1 Chap 9 (6/5e): ER to Relational Transformation Prof. Steven A. Demurjian, Sr. Computer Science & Engineering Department The University.

CSE 4701

Chapter 9-1

Chap 9 (6/5e): ER to Relational Transformation

Prof. Steven A. Demurjian, Sr. Computer Science & Engineering Department

The University of Connecticut191 Auditorium Road, Box U-155

Storrs, CT [email protected]

http://www.engr.uconn.edu/~steve(860) 486 - 4818

The Majority of these slides are being used with the permission of Dr. Ling Lui, Associate Professor, College of Computing, Georgia Tech.

Other slides (figures) have been adapted from the AWL web site for the textbook.

CSE 4701

Chapter 9-2

Designing a Relational DB Schema Defining Relations

Deciding which Attributes belong Together in Each Relation

Choosing Appropriate Names for the Relations and Their Attributes

Specifying the Domains and Data Types of the Various Attributes

Identifying the Candidate Keys and Choosing a PK for Each Relation, and Specifying All Foreign Keys

Two Techniques for Relational Schema Design Using ER-to-Relational Mapping (Chapter 9) Relational Normalization Theory (Chapter 14)

CSE 4701

Chapter 9-3

Design Process - Where are we?Conceptual

Design

ConceptualSchema

(ER Model)

LogicalDesign

Logical Schema(Relational Model)

Step 1: ER-to-Relational Mapping

Analysisof Schema

Step 2: Normalization

Normalized Schema

CSE 4701

Chapter 9-4

ER-to-Relational Mapping Algorithm

Step 1: For Each Regular Entity Type E Create a Relation RE

Include only the Simple Attributes of a Composite Attribute

Step 2: For Each Weak Entity Type W with Owner Entity Type E Create a Relation RW

Include as Attributes All Simple Attributes of W Primary Key attribute(s) of the Relation that Corresponds

to W’s Owner Entity Type E

CSE 4701

Chapter 9-5

ER-to-Relational Mapping Algorithm

Step 3: For Each 1:1 Relationship Identify the Relations R1 and R2

Include as Foreign Key of one Relation the Primary Key of the Other Relation

Step 4: For each Regular 1:n Relationship Include as Foreign Key in the Entity Type at the n-

side of the Relationship, the Primary Key of the Entity Type at the 1-side of the Relationship

CSE 4701

Chapter 9-6

ER-to-Relational Mapping Algorithm

Step 5: For Each Binary n:m Relationship Create a New Relation, whose Attributes Include

All Simple Attributes of the n:m Relationship as Non-key Attributes

PKs of the Relations that Represent the Participating Entity Types, as FK Attributes in this New Relation

Step 6: For Each Multi-valued Attribute A Create a New Relationship R that Includes

An Attribute Corresponding to AThe PK Attribute of the Relation Whose Corresponding

Entity Type or Relationship Has A as an Attribute

CSE 4701

Chapter 9-7

ER-to-Relational Mapping Algorithm

Step 7: For Each n-ary Relationship R, n>2 Create a New Relation to Represent R

Step 8: Convert Each Specialization for Superclass C with Attributes {k, A1, …, An} (k is the PK), where C has n Subclasses {S1, ..., Sn} Create a Relation Si for each Subclass Entity

(1<= i <= n) with Attributes Attrs(Si) = {k} {attributes of Si}, and PK{Si} = k

Note that the Relation for C was created in an Earlier Step

Note also that there are Three Other Options for Mapping Specialization Hierarchies

CSE 4701

Chapter 9-8

Recall our Ongoing Example

EMPLOYEE

PROJECT

Responsibility

Duration

BudgetProjectName

Project No

Employee No

EmployeeName

SalaryTitle

WORKS ON

Address

CityApt. #

Street #

Location

1

N

MANAGES

BALANCEExpenses

1RECORDSACCOUNT

Income

1

DateAmount

SUPPLYSUPPLIER

Supplier No SupplierName

LocationCredit

N M

PART

LPart No

PartName

Weight

Color

CONTAIN

M N

Made-up of Consists of

1

1

QTY

SALESPERSON

Car

Region

SECRETARY

Specialty

Office

ENGINEER

Project

Office

Acount #

d

o

MANUFACTURED_PART PURCHASED_PART

Batch No Drawing No Price

CSE 4701

Chapter 9-9

Can we Transition the Previous ER to ...

Note that there areno subclasses here!

CSE 4701

Chapter 9-10

Step 1 - Handling Entities

For Each Regular Entity Type E in the E-R Schema, Create a Relation R Include as Attributes in R Only the Simple

Attributes of E For Composite Attributes of E, Include Only their

Constituent Simple Attributes in R The Key of E Becomes the PK of R

If There is More Than One Key Attributes of E, Then Choose One as the Primary Key of R

For Multi-Valued Attributes – Create a new Table in Step 6

CSE 4701

Chapter 9-11

Create the Following Strong Entity Types:

Create Four Corresponding Relations with Attribute Keys as PKs

Step 1 – Example

SUPPLIER

Supplier No SupplierName

LocationCredit

PROJECT

BudgetProjectName

Project No

Location

PART

Part No

PartName

Weight

Color

EMPLOYEEEmployee No

EmployeeName

SalaryTitle

Address

CityApt. #

Street #

CSE 4701

Chapter 9-12

The Keys are Underlined

EMPLOYEE(ENO, ENAME, TITLE, SALARY, APT#, STREET, CITY)

PROJECT(PJNO, PNAME, BUDGET)

SUPPLIER(SNO, SNAME, CREDIT, LOCATION)

PART(PNO, PNAME, WGT, COLOR)

Notes:

LOCATION is Not Included in PROJECT – handled later in Step 6

ACCOUNT is Weak and ENGINEER, SECRETARY, and SALESPERSON are Subclasses

Step 1 – Example

CSE 4701

Chapter 9-13

Step 2 – Weak Entities

For Each Weak Entity Type W Associated with the Strong Entity Type E in the E-R Schema, Create a Relation R Attributes of R are the Simple Attributes of W (or

the Simplified Versions of Composite Attributes) Include Among the Attributes of R all of the Key

Attributes of Strong Entity E These are the Foreign Keys of R

The PK of R is the Combination of the PK of E and the Partial Key of W

CSE 4701

Chapter 9-14

Create relation ACCOUNT as follows

ACCOUNT(PJNO, ACNO, INCOME, EXPENSES)

Note that ACNO Corresponds to Account# on ACCOUNT

PJNO Corresponds to ProjectNo on PROJECT

We’ll Handle Records Relationship in Separate Step

foreign key

Step 2 – Example

Expenses

ACCOUNT

IncomeAcount #

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Chapter 9-15

If there was a Dependent … Create a Dependent Table:

DEPENDENT(ENO, NAME, SEX, BIRTHDATE, RELATIOSHIP)

Primary Key from EMPLOYEE (ENO) PLUST DEPENDENT (NAME)

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Chapter 9-16

Step 3 – 1:1 Relationships

For Each 1:1 Relationship R in E-R Schema where the Two Related Entities are E1 and E2

Let Relations S and T Correspond to E1 and E2 Respectively Choose One of the Relations, Preferably One Whose

Participation in R is Total (Say S) Include in S as a FK, the PK of T

If there are Attributes Associated With the Relationship R, Include Them in S

You May Want to Rename the Attributes When You Do This

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Chapter 9-17

For 1:1 Relationship MANAGES between the EMPLOYEE and PROJECT Entities Choose PROJECT as S, Since its Participation in

the MANAGES relationship is TotalInclude in PROJECT the PK of EMPLOYEE

PROJECT(PJNO, PNAME, BUDGET) BecomesPROJECT(PJNO, PNAME, BUDGET, MGR)

Step 3 – Example

MANAGES1

1PROJECT

BudgetProjectName

Project No

Location

EMPLOYEEEmployee No

EmployeeName

SalaryTitle

Address

CityApt. #

Street #

CSE 4701

Chapter 9-18

For 1:1 Relationship RECORDS between PROJECT and ACCOUNT Entities: Choose ACCOUNT as S (ACCOUNT is a Weak

Entity, so this is the only choice that makes sense) Include PJNO (done in step 2) and BALANCE

ACCOUNT(PJNO, ACNO, INCOME, EXPENSES) BecomesACCOUNT(PJNO, ACNO, INCOME, EXPENSES,

BALANCE)

Step 3 – Example

RECORDS1 1

PROJECT

BudgetProjectName

Project No

Location BALANCE

Expenses

ACCOUNT

IncomeAcount #

CSE 4701

Chapter 9-19

For Each Regular (Non-weak) Binary 1:N Relationship Type R in the E-R Schema Identify the Relation S that Corresponds to the

Entity Type at the N-side of the Relationship Let the Other Relation on the 1-side be T

Include in S as a Foreign Key, the Primary Key of TIf There are Attributes Associated with the Relationship

R, Include them in S as well

Step 4 – 1:N Relationships

CSE 4701

Chapter 9-20

Step 4 – Example

We have only the WORKS ON relationshipDefined between PROJECT and EMPLOYEE N side of the Relationship is EMPLOYEE 1 side of the Relationship is PROJECT

WORKS_ON1

N

PROJECT

BudgetProjectName

Project No

Location

EMPLOYEEEmployee No

EmployeeName

SalaryTitle

Address

CityApt. #

Street #

Responsibility

Duration

CSE 4701

Chapter 9-21

Step 4 – Example

Include in EMPLOYEE Primary Key (PJNO) of PROJECT Attributes of the WORKS ON relationship

(Duration & Responsibility) This is Since EMPLOYEE WORKS ON Only 1

PROJECT

EMPLOYEE(ENO, ENAME, TITLE, SALARY, APT#, STREET, CITY)

BecomesEMPLOYEE(ENO, ENAME, TITLE, SALARY, APT#,

STREET, CITY, PJNO, DURATION, RESP)

CSE 4701

Chapter 9-22

Step 5 – M:N Relationships

For each Binary M:N Relationship Type R Connecting E1 and E2 in the ER schema, create a relation S: Include as FKs of S, the PKs of the two relations

that correspond to E1 and E2These Attributes, Together, Form the primary key of SAlso Include in S any Attributes of the Relationship R

CSE 4701

Chapter 9-23

Step 5 – M:N Relationships

We have one M:N Relationship: CONTAIN, which is a Recursive Relationship over the PART Entity

We create the following relation:

CONTAIN(PNO, CPNO, QTY)

Recursive Relationship Requires us to Distinguish the Part No as PNO and CPNO

PART

Part No

PartName

Weight

Color

CONTAIN

M N

Made-up of Consists of

QTY

CSE 4701

Chapter 9-24

For each Multivalued Attribute A, Create a New Relation R The Attributes of R are A (if composite, then use

only the simple components) Include in R the PK K of the entity that contained A The PK of R then becomes K and A together

Recall that Multivalued Means that a Given Attribute has Multiple Values in the Entity Previous Degrees of a Student {Bachelors, Masters} Can have Neither, One, or Both for each Student

Step 6 – Multivalued Attributes

CSE 4701

Chapter 9-25

In our Example, we create One New Relation for the Multivalued Attribute LOCATION in PROJECT

This Relation is Created as Follows:

LOC (PJNO, LOCATION)

That is, Storrs, Hartford, etc., for Project P1

Step 6 – Multivalued Attributes

PROJECT

BudgetProjectName

Project No

Location

The Same Project (Project No) can be Spread Across Multiple Locations

CSE 4701

Chapter 9-26

For Each Higher Order Relationship Type R Connecting E1, E2, …, En in the E-R schema, Create a relation S Include in S the PKs of the Relations Corresponding

to E1, E2, …, En Also Include in S any Attributes of R The PK of S is the Combination of the PKs of the

Relations Corresponding to E1, E2, …, En

Step 7 – Higher Order Relationships

CSE 4701

Chapter 9-27

PROJECTSUPPLYSUPPLIERN M

PART

L

Step 7 – Example

The Only High-Order Relation is SUPPLY between SUPPLIER, PROJECT and PART Create Relation SUPPLY where Amount and Date

were Attributes Defined on SupplySUPPLY(SNO, PJNO, PNO, AMOUNT, DATE)

DateAmount

CSE 4701

Chapter 9-28

For Each Specialization with m Subclasses {S1, …, Sm} and Generalized Superclass C, where the Attributes of C are {k, A1, …, An} (k is the PK), Convert According to the Following:

Option 1: General Case:Create a Relation T for C with Attributes

{k, A1, …, An} and use k as the PK

Create one Relation Ui for each SiInclude in Ui all the attributes of Si and kUse k as the primary key of Ui.

Step 8 – Specialization

CSE 4701

Chapter 9-29

Option 2: No Superclass Relation:Create One Relation Ui for each Si.

Include in Ui all Attributes of Si and {k, A1, …, An}

Use k as the Primary Key of Ui

Option 3: For Disjoint Subclasses:Create a Single Relation U which Contains all the

Attributes of all Si and {k, A1, …, An} and t

Use k as the primary key of Ui

The Attribute t Indicates the Type Attribute According to which Specialization is Performed

Step 8 – Specialization (cont’d)

CSE 4701

Chapter 9-30

Option 4: For Overlapping Subclasses:Create a single relation U which contains all

Attributes of all Si and all Attributes of C ({k, A1, …, An}) and {t1, …, tm}

Use k as the Primary Key of Ui

The Attributes ti are Boolean Valued, Indicating if a Tuple Belongs to Subclass Si

Note: May Generate a Large Number of Null Values in the Relation

Step 8 – Specialization (cont’d)

CSE 4701

Chapter 9-31

Specialization of EMPLOYEE EMPLOYEE Already Exists; option 2 is not valid Specialization is Disjoint; option 4 is not valid Option 1:

EMPLOYEE(ENO, ENAME, TITLE, SALARY, APT#, STREET, CITY, PJNO, DURATION,

RESP)

ENGINEER (ENO, PROJECT, OFFICE)

SECRETARY(ENO, OFFICE, SPECIALTY)

SALESPERSON(ENO, CAR, REGION)

Option 3:EMPLOYEE(ENO, ENAME, TITLE, SALARY, APT#,

STREET, CITY, PJNO, DURATION, RESP, TYPE, PROJECT, OFFICE, SPECIALTY, CAR, REGION)

Step 8 – Example

CSE 4701

Chapter 9-32

Step 8 – Example (cont’d) Specialization of PART

Relation PART Already Exists; Option 2 is not valid Specialization is Overlapping;Option 3 is not valid Option 1:

PART(PNO, PNAME, WGT, COLOR) MANUFACTURED_PART(PNO, BATCH#,

DRAWING#)PURCHASED_PART(PNO, PRICE)

Option 4:PART( PNO, PNAME, WGT, COLOR,

MAN, BATCH#, DRAWING#, PURC, PRICE)

Note that MAN and PURC are Boolean Flags

CSE 4701

Chapter 9-33

EMPLOYEE(ENO, ENAME, TITLE, SALARY, APT#, STREET, CITY, PJNO, DURATION, RESP)

PROJECT(PJNO,PNAME,BUDGET,MGR)

SUPPLIER(SNO,SNAME,CREDIT,LOCATION)

PART(PNO, PNAME, WGT, COLOR, MAN, PURC, BATCH#, DRAWING#, PRICE)

ENGINEER(ENO, PROJECT,OFFICE)

SECRETARY(ENO, OFFICE, SPECIALTY)

SALESPERSON(ENO, CAR, REGION)

SUPPLY(SNO, PJNO, PNO, AMOUNT,DATE)

LOC(PJNO, LOCATION)

CONTAIN(PNO, CPNO,QTY)

ACCOUNT(PJNO, ACNO, INCOME, EXPENSES, BALANCE)

Final Set of Relations

CSE 4701

Chapter 9-34

Step 8 – Option 1 Example

CSE 4701

Chapter 9-35

Step 8 – Option 2 Example

CSE 4701

Chapter 9-36

Step 8 – Option 3 Example

Secretary Tech Engr

Where JobType Playing theRole of a Type Attribute

CSE 4701

Chapter 9-37

Step 8 – Option 4 Example

Boolean

BooleanMflag - are thenext three fields

active - thenManufactured_Part

Pflag - are thenext three fields

active - thenPurchased_Part

CSE 4701

Chapter 9-38

Step 8 - Recall Specialization Lattice

Person

Employee Alumni Student

Staff Faculty StudAsst Grad UnderGrad

ResAsst TeachAsst

CSE 4701

Chapter 9-39

Step 8 - Corresponding Relations

CSE 4701

Chapter 9-40

Step 8 - Recall Categories - Figure 4.8

CSE 4701

Chapter 9-41

Step 8 - Recall Categories - Figure 4.8

CSE 4701

Chapter 9-42

Step 8 - Corresponding Relations

CSE 4701

Chapter 9-43

In Class Exercise

How would we Translate Solutions from Homework 1? ER Solution for Problem 1.1? EER Solution for Problem 1.2?

CSE 4701

Chapter 9-44

ER for Problem 1.1

Phone#

Patient

Drug

Physician

name

address email

SSN

status

price

name

expiration

name

email

address

specialtyPrimary

N 1

DEA#

Prescribes

refills N

N

dosage

dateFill

requirementpattern

Sold By

Purchasing Contract

start_date end_date

CSE 4701

Chapter 9-45

EER for Problem 1.2

Patient

Drug

PhysicianSSN

status

price

name

expiration

specialtyPrimary

N 1

Prescribes

refills N

N

dosage

dateFill

requirementpattern

Sold By

Purchasing Contract

start_date end_date

Person

Drug Prescriber

DEA#

CSE 4701

Chapter 9-46

EER for Problem 1.2

Notice Movement of Common Attributes to Person and DEA number to Presriber

“Person” is a parent of both Patient and Physician and Physician also a Sub-entity of Drug Prescriber

Person

phone

name

address

email

Drug Prescriber

Physician

Physician

DEA#

CSE 4701

Chapter 9-47

Patient

Drug

PhysicianSSN

status

price

name

expiration

specialtyPrimary

N 1

Prescribes

refills N

N

dosage

dateFill

requirementpattern

Sold By

Purchasing Contract

start_date end_date

Person

Drug Prescriber

DEA#

name

emailaddress

CSE 4701

Chapter 9-48

What are Steps STEP 1: CONVERT EACH ENTITY

CREATE A TABLE STEP 2: WEAK ENTITIES

CREATE TABLE LINK TO STRONG STEP 3: 1-1 RELATIONSHIPS

INCLUDE FKEY IN ONE OF TWO STEP 4: 1- MANY

INCLUDE REFERNCE FKEY TO MANY SIDE STEP 5: MANY-MANY

NEW TABLE STEP 6: MULTI-VALUED

NEW TABLE STEP 7: N-ARY (3 or MORE)

NEW TABLE STEP 8: INHERITANCE

CSE 4701

Chapter 9-49

Concluding Remarks What have we Learned in Chapter 9?

Transition from a Conceptual Schema (ER) to Set of Relations

Transition is Necessary as First Step in the Relational Database Design Process

Result of Transition is a Set of Relations that Capture the Entities and “Relationships” in ER Diagram

Objective: Flatten out the ER into Relations How is Chapter 9 Related to the Semester Project?

Phase II in the Semester Project is to Transition your ER Diagram into a Set of Relational TablesStep 1: ER to Relational Transformation (Chapter 9)Step 2: Relational Normalization (Chapter 14)