Unit3 Mapping ERDs into Relations.pdf

8/22/2019 Unit3 Mapping ERDs into Relations.pdf

1/53

Unit 3 :

Mapping ERDs into Relations

Pratian Technologies (India) Pvt. Ltd.www.pratian.com


2/53

Topics

RDBMS Terminology

Primary Key

Foreign Key

Candidate Key

Integrity Constraints

Copyright 2012 Pratian Technologies

www.pratian.com


3/53

Purpose information requirements structure

Deliverable detailed design specifications

Project Identification

and Selection

Project Initiation

and Planning

Analysis

Logical Design

Logical Design

SDLC revisited


www.pratian.com

Maintenance

Database activity

logical database design

Physical Design

Implementation

Maintenance


4/53

Sample Database Table

C

a

r

d

Attributes


www.pratian.com

Relation

Degree

i

n

a

li

t

y

Tuples

Instance


5/53

RDBMS Terminology

Formal Relational Term Informal Equivalents

Relation Table

Tuple Row, Record

Cardinality Number of Rows

Attribute Column Field


www.pratian.com

Degree Number of Columns

Primary Key Unique Identifier

Domain Set of legal values


6/53

Candidate Key, Primary Key, Alternate Key

A candidate key is an attribute that can uniquely identify arow in a table.

ELEMENT

Symbol Name AtomicNo MeltingPoint BoilingPoint

Al Aluminium 13 933 2792

Fe Iron 26 1811 3134


www.pratian.com

Ni Nickel 28 1728 3186

Cu Copper 29 1357 3200

Ag Silver 47 1235 2435

Au Gold 79 1337 3129


7/53

Definitions

Primary Key An attribute ( or combination of attributes ) that uniquely

identifies each row in a relation

Composite key

A primary key that consists of more than one attribute


www.pratian.com


8/53

Foreign Key

Attribute or attribute combination of one table whosevalues are required to match those of the primary key of

some other table

Each Foreign key represents a relationship between twoentity types.


www.pratian.com


9/53

Foreign Key - Definition

They are added to relations as we go throughmapping process

They allow the relations to be linked together

A relation can have several foreign keys


www.pratian.com

Generally there will be a foreign key from each table arelation is related to

Foreign keys are usually show in italics or wigglyunderline


10/53

AUTHORS TABLE

AUTHORID NAME CITY COUNTRY

A1 SHOBHA DE MUMBAI INDIA

PUBLISHER TABLE

Foreign Key


www.pratian.com

_

P1 MCGRAW HILL NEW YORK U.S.A

WORK TABLE

AUTHORID PUB_ID TITLE

A1 P1 SISTERS


11/53

Integrity Constraints

Domain Constraints All the values that appear in a column must be taken

from the same domain

Domain definition consists of the following components

Domain Name

Meaning

Data type

Size/ Length


www.pratian.com

Allowable values or range

Entity Integrity Primary key

Referential Integrity

Involves foreign key

Operational Constraints Implement real world limitations


12/53

Transforming E R Models to Relations

name

sex

name dateofbirth

empnodeptid

EMPLOYEE

EMPLOYEE ( empno , name, sex, dateofbirth, deptid)


www.pratian.com

EmpNo Name Sex DateOfBirth DeptId

1 Mohan M 01-01-1978 10

2 Sarvesh M 12-01-1980 20


13/53

Properties of a Relation

Each entity or a table in a database has a uniquename

An entry at the intersection of each row and column

is atomic. There can be no multivalued attributes in arelation

Each row is unique.


www.pratian.com

ac a r u e or co umn w n a a e as a un quename.

The sequence / arrangement of columns isinsignificant

The sequence / arrangement of rows is insignificant


14/53

Mapping the ER Model

Mapping Strong entity

name

deptname costcenter

deptid

DEPARTMENT

DEPARTMENT ( DeptId, DeptName, CostCenter)


www.pratian.com


15/53

Mapping 1:1 Relationship

Mandatory at both ends

Mandatory at one end and optional at theother


www.pratian.com

Optional at both ends


16/53

Mandatory at both ends Option 1

EMPLOYEE (empno, name)

CONTRACT (contractno, startdate, duedate)

EMPLOYEE CONTRACThas


www.pratian.com

Amalgamated into one as

EMPLOYEE (empno, name, contractno, startdate, duedate)


17/53






www.pratian.com

The same can be kept apart using Foreign Key

EMPLOYEE (empno, name, contractno)



18/53






www.pratian.com

r

EMPLOYEE (empno, name)CONTRACT (contractno, startdate, duedate, empno)


19/53

Mandatory at one end and Optional at other end





www.pratian.com

Amalgamated into one as

EMPLOYEE (empno, name, contractno, startdate,duedate)


20/53



EMPLOYEE (empno, name) CONTRACT (contractno, startdate, duedate)


www.pratian.com

The same can be kept apart using Foreign KeyEMPLOYEE (empno, name, contractno)CONTRACT (contractno, startdate, duedate)

Map the foreign key into Employee - the key is null foremployee without a contract. Incorrect Design


21/53

FK in EMPLOYEE

Empno Name Contract No

10 Gordon 1

11 Andrew NULL

EMPLOYEE

CONTRACT


www.pratian.com

Contractno StartDate DueDate

1 1st

Jan 2007 10th

Oct 2007


22/53



EMPLOYEE (empno, name)CONTRACT (contractno, startdate, duedate)


www.pratian.com

EMPLOYEE (empno, name)CONTRACT (contractno, startdate, duedate, empno)

Map the foreign key into Contract

empno is mandatory thus never null.


23/53

FK in CONTRACT

Empno Name

EMPLOYEE

So for 1:1 optional relationships, take the primary keyfrom the mandatory end and add it to the optional end

as a foreign key.


www.pratian.com

11 Andrew

CONTRACT

Contractno StartDate EndDate Empno

1 1st Jan 2007 10th Oct 2007 10


24/53

Optional Participation at Both Ends


www.pratian.com

Such examples cannot be amalgamated as you

could not select a primary key.


25/53

Mapping 1:M Relationships

DEPARTMENT (Deptid, name, type, location) EMPLOYEE (empno, name)

DEPARTMENT EMPLOYEEhas


www.pratian.com

After Mapping the foll relations are produced

DEPARTMENT (Deptid, name, type, location)EMPLOYEE (empno, name, Deptid)


26/53

Mapping 1:M in Unary Relationships

Employee manages employees


www.pratian.com

Employee(employee_no, manager_no, name,...)

Foreign keyPrimary key


27/53

EMPNO ENAME JOB MGR SAL

7369 SMITH CLERK 7902 1800

7499 ALLEN SALESMAN 7698 1600

7521 WARD SALESMAN 7698 1250

7566 JONES MANAGER 7839 2975

7654 MARTIN SALESMAN 7698 1250

7698 BLAKE MANAGER 7839 2850

Mapping 1:M in Unary Relationships


www.pratian.com

7788 SCOTT ANALYST 7566 3000

7839 KING PRESIDENT 6000

7844 TURNER SALESMAN 7698 9300

7876 ADAMS CLERK 7788 2100

7900 JAMES CLERK 7698 1950

7902 FORD ANALYST 7566 7777

7934 MILL CLERK 7782 7654


28/53

Mapping M:N Relationships

A new table has to be created to map M : N relations

AUTHOR PUBLISHER

M N


www.pratian.com

authorid name

city country

pub_id name

city country


29/53

Mapping N:M Relationships

AUTHOR PUBLISHERAuthor_Publisher1 N N 1

authorid pub_id title


www.pratian.com

authoridname

city country

pub_id name

city country


30/53

Mapping N:M Relationships

AUTHORS TABLE

AUTHORID NAME CITY COUNTRY

A1 SHOBHA DE MUMBAI INDIA

PUBLISHER TABLE

PUB ID NAME CITY COUNTRY


www.pratian.com

_

P1 MCGRAW HILL NEW YORK U.S.A

WORK TABLE

AUTHORID PUB_ID TITLE

A1 P1 SISTERS


31/53

Summary

1-1 relationshipsDepending on the requirement of the relationship,the entities are either combined or the primary keyof one entity type is placed as a foreign key in the

other relation.

1-m r l i n hi


www.pratian.com

The primary key from the one side is placed as aforeign key in the many side.

m-n relationshipsA new relation is created with the primary keysfrom each entity forming a composite key.


32/53

Lets check our understanding!!!


www.pratian.com


33/53

Primary Key

Forei n Ke

Identify keys in these relations


www.pratian.com

(implements 1:N relationship

between customer and order)

Combined, these are a composite

primary key (uniquely identifies the

order line)individually they are

foreign keys (implement M:N

relationship between order and product)


34/53

(a) CUSTOMERentity type withsimple

attributes

Write Customer relation for the foll.


www.pratian.com

(b) CUSTOMER relation


35/53

(a) CUSTOMERentity type withcompositeattribute

Map the foll into a relation


www.pratian.com

(b) CUSTOMER relation with address detail


36/53

Map the foll. into relations

(a)


www.pratian.com1tomany relationship between original entity and new relation

Multivalued attribute becomes a separate relation with foreign key(b)


37/53

Map the foll ERD


www.pratian.com


38/53

NOTE: the domain constraint

for the foreign key shouldNOT allow null value if

DEPENDENT is a weak

entity


www.pratian.com

Foreign key

Composite primary key


39/53

Map the Relationship between customers and orders


www.pratian.com

Note the mandatory one


40/53

Mapping the relationship

Again, no null value in the

foreign keythis is


www.pratian.com

because of the mandatory

minimum cardinality

Foreign key


41/53

Map an M:N relationship into relations

E-R diagram (M:N)


www.pratian.com

Hint :The Supplies relationship will need to become a separate relatio


42/53

Solution: Three resulting relations

Composite primary key


www.pratian.com

intersectionrelation

Foreign key

Foreign key

M bi l i hi


43/53

Map a binary 1:1 relationship

In_charge relationship


www.pratian.com

S l ti R lti l ti


44/53

Solution: Resulting relations


www.pratian.com

M th f ll ERD i t l ti


45/53

Map the foll ERD into relations


www.pratian.com


46/53


www.pratian.com

M h f ll ERD i i i i h id ifi


47/53

Map the foll ERD : an associative entity with an identifier

Associative entity


www.pratian.com

Three resulting relations


48/53

Three resulting relations


www.pratian.com

Map a unary 1:N relationship


49/53

Map a unary 1:N relationship

(a) EMPLOYEE entity with

Manages relationship


www.pratian.com

(b) EMPLOYEErelation with

recursive foreign

key

Map a unary M:N relationship


50/53

Map a unary M:N relationship

(a) Bill-of-materials

relationships (M:N)


www.pratian.com

(b) ITEM and

COMPONENT

relations

Map a ternary relationship


51/53

Map a ternary relationship

Ternary relationship with associative entity


www.pratian.com

Solution


52/53

Solution


www.pratian.com

Remember that theprimary key MUST be

unique

Question time


53/53

Please try to limit the questions to the topics discussed during the session. Thank you.

Question time


www.pratian.com

Date post:	08-Aug-2018
Category:	Documents
Upload:	divyasindhuri
View:	226 times
Download:	0 times

Unit3 Mapping ERDs into Relations.pdf

Documents