ER_Model Presenatation

1ER Model

2Database design- steps

Requirement Analysis

Conceptual Database Design ER Diagram

Logical Database Design

Additional design components like views,

stored procedures, triggers etc.

Converting ER Diagram

into RDBMS tables etc.

Later

3ER Model

ER data model allows us to conceptually understand the data of the real world enterprise which we want to store in terms of their relationships.

This model is realized by diagrammatically representing the collection of data and their relationship. There are two established versions for entity relationship diagram (ERD):

Chens notation and Crows foot notation. As stated earlier, this is done in conceptual database design phase. As stated earlier, this is done in conceptual database design phase.

Our focus

4Defining Entity

Entity: It is an object that is distinct and unique. Examples: a student, a keyboard, a college etc.

Entity set: A collection of similar entities is entity set. Examples : Students, Colleges

Attributes: Properties that describe an entity is attribute. All entities in the entity set have same attributes (but the values of the attribute may be different). For example, a student will have the attribute may be different). For example, a student will have registration number, name and address as attributes.

5Primary Key A minimal set of attributes that uniquely identifies an entity is called a

candidate key.

An entity can have many candidate keys. For example, for a student entity, if we assume that students have unique names, both registration no. and name are candidate keys.

One among the candidate keys is chosen to be a primary key. A primary key should not be null.

A composite key is a primary key with more than one attribute.

A super key is a set of attributes which contains the primary key.

6Representing an entity in Chens notation

Students

regNo

name

Attributes

Primary key

address

Courses

streamId

title

noOfSems

Entity Set

7Relationship

Relationship is the association between entities or entity sets. For example between two entities student and course, the relationship is a course enrolls for many students.

Relationships may or may not also have attributes. For example, if we were to maintain enrollment date, then the relation enrolls will we were to maintain enrollment date, then the relation enrolls will have an attribute enrollment-date.

Relationship set is a collection of similar relationships.

8Binary Relationship Example

Subject Is Taught Teacher

teacherIdtitle

1 1

Mapping/Connectivity

nameaddresssubId

Relationship SetOne to One

9Binary Relationship Example

Courses Has Students

regNonoOfSems

1 N


nameaddressstreamId title

Relationship SetOne to Many

10

Binary Relationship Example

Customer Bank Account

acctNoaddress

M N


owns

acctTypebalancecustId name

Relationship Set

Many to Many

11

Relationship with attributes


regNonoOfSems

1 N



Relationship Set

enrollment-date

Attribute of relationship

Binary Relationship

12

Cardinality

regNoCardinality

Cardinality is used to specify number of entity occurrences with one occurrence of related entity. A course can have a minimum of 1 and a maximum of 35 students. A student can take a maximum of 6 and a minimum of 1 course.


regNo


noOfSems

enrollment-date

(1,35)(1,6)

Cardinality

13

Example of a Ternary relationship

Employees DepartmentsWorks-In

dateOfJoining

deptIdempId

N M

Location

namename

addresscapacity

locId

P

14

Example of a Unary relationship

CustomercustId

address

referred CustomercustId

name

referred byN

1

15

Key Constraints on relationship Consider a restriction where a student can join only one course. This is an

example of a key constraint.

In the below diagram the directional arrow ensures that there is only one instance of student in the relationship set Has. In other words, given a student, has relationship can be uniquely determined.


regNo

name

addressstreamId

title

noOfSems

1 N

enrollment-date

Directional arrow

16

Customer buy ArtPiecetitle

custIdaddress

1 N

Directional arrow

itemId

price

Customer buy ArtPiecename

date-of-purchaselastprice

17

Participation constraints

Total participation: If all entities in an entity-set need to be in the relationship set then the entity is in total participation with respect to relationship.

Example: Every employee works in at least one department. Each department has at least one employee. Therefore both Employee and Department entities in Works-In relationship is total.

Partial participation: A participation that is not total is partial .

18

Example of a total participation


dateOfJoining

deptIdempId

location

namename

addresscapacity

locIdIndicate total participation

or

19

Modeling Attributes

20

Single-Valued Attributes

An attribute which has only one value.

All the attributes that we have seen so far were single valued attribute.

Employees

name single-valued attribute

21

Composite Attribute

A composite attribute is an attributes that is made up of more than one attribute.

For example address can be thought of as having more than one attribute.

address

house number street number

colony or area

city or towndistrict

house number

state

country

Employees

composite attribute

22

Multi-Valued Attribute

A multi-value attribute is an attribute which can have multiple values.

phone_numbers

Employeesmulti-valued attribute

23

Derived Attribute

A derived attribute is an attribute whose value is determined or computed using existing values of the other attributes (or otherwise also called stored attribute).

While the value of the composite attribute for a row is computed as concatenation of the values of a set of attributes of the same row, the concatenation of the values of a set of attributes of the same row, the derived attribute can be calculated based on values of attributes in multiple rows also( example sum of gross_salary of all entities in Employee entity set)

24

Example

Employee

gross_salary

net_salary

derived attributedeductionsgross_salary

stored attribute

derived attribute

25

Weak Entities

A weak entity is an entity that cant be uniquely identified by its own attributes alone, and therefore must use as its primary key both its own attributes and the primary key of an entity it is related to.

In other words, a weak entity cannot exist without the entity it is related to (owner entity).The relationship between owner entity and weak entity is one-to-many.

26

Weak Entity example

Assume a shopping application. A customer orders for many items. We have 2 entities to maintain customer order. Orders entity: records the order details like order number, order

date and customer id Order-Items: records the items pertaining to the order. Order-Items: records the items pertaining to the order. Order-Items entity is a weak entity.

27

Orders Order-Itemscontains

A weak entity set diagram

itemNocustId

partial key

1 n

Invariably the entity

will be in total

participation

orderDateorderNo

noOfPieces

contains

Order-Items

or or

Identifying

relationship

28

Hierarchy

The entities can be classified as general type and specific type.

IS-A relationship.

For example, an Employee can be a programmer or a manager.

IS-A relationship.

Employeename empId

IS-A

Programmer Marketing

Current-Project

Main-Role

area

num-of-contracts

specia

lizatio

ng

e

n

e

r

a

l

i

z

a

t

i

o

n

IS-A relationship.

29Redundant relationship problem and Aggregation

Consider a relationship where employee works on an assignment and may use machinery.

namejoiningDateempId

Employee works Project

usesMachinery

machineID

purchaseDateredundant relationships

hours

30

Aggregation

Solution is to use aggregation. Aggregation is a relationship between collection of entities and relationships.

Aggregation allows us to indicate that a relationship set participates in another relationship set.

Use aggregation when we need to have a relationship among Use aggregation when we need to have a relationship among relationship.

31

Employee

namejoiningDate

works Project

aggregation

empId

uses Machinery machineID

purchaseDate

aggregation

hours

32

Entering Into Relational ModelEntering Into Relational Model

33

The main construct for relation model rests on the relation (table). A relational database is a collection of relations.

The degree ( or arity) of a relation is the number of fields in a relation. The cardinality of a relation is number of tuples in it.

More terms

The cardinality of a relation is number of tuples in it.

34

Integrity Constraints

An integrity constraint is a condition or a rule specified on the table which restricts the kind of data that can be stored in a table.

These rules thereby ensures that data entered in the database is accurate and valid.accurate and valid.

DBMS ensures that the constraints defined in the schema is strictly adhered to when ever or however data enters into the database.

35

Types of Integrity Constraints Entity integrity allows no two rows with the same identity in a table.

Primary Key and Unique constraint are used to enforce entity integrity.

Referential integrity allows only the consistent values for certain fields across the related tables. Foreign Key is used to enforce referential integrity.integrity.

Domain integrity allows only predefined values for the attributes.

User-defined integrity allows only what you predefine. Example: Null constraint.

Define in the next slide

Later

Constraints for candidate keys which are not primary key

36

Foreign Key A foreign key is a reference to a primary key in another table.

Therefore referential integrity is ensuring that the foreign key has only those data values that correspond to the primary key data values of another table.

DeptName Manager

Marketing EMP100

Training EMP200

DepartmentID Name

EMP100 Rama

EMP101 Rahim

EMP200 Raghu

EmployeeForeign key

Primary key

Enforcing referential integrity

37

Other advantages of foreign key Specifying foreign key also allows us to specify what action should be

taken when the corresponding primary key data is updated or deleted. Action could be either

NO ACTION: Dont allow update or deletion of the primary whose value is referenced by the foreign key.

CASCADE: Delete or Update foreign key also when the corresponding primary key is changed.

SET NULL: set null values to foreign key values when the corresponding primary key value is changed.primary key value is changed.

38

Null values and Keys

A column which does not have any value has Null Value.

For attributes which should not have null value, NOT NULL constraints can be specified.

For a foreign key null value is allowed.

A primary key cannot be null.

Unique key can be null.

39

Translating E-R Diagram into Relational Model

40

Modeling Entity Set

Model entity sets to tables with primary key constraints.

noOfSems

streamId title noOfSems

Courses

Courses

streamId

title streamId title noOfSems

123 B.Tech 8

124 B.E. 8

41

Modeling Relationship-set

Modeling One-to-One relationship

Modeling One-to-Many relationship

Modeling Many-to-Many relationship

Modeling relationship with attributes

42

One-to-One into Relational Model

Primary Key of any of the entity set can become foreign Key of the other entity set.

teacherIdtitle

Subject Is Taught Teacher

nameaddresssubId

title

1 1

43One-to-One into Relational Model

subId title teacherId

S101 Java EMP103

S102 C EMP102

S103 OOPS and UML EMP101

Subject

S103 OOPS and UML EMP101

teacherId name address

EMP101 Mona Lisa XXX YY

EMP102 Lora Nillie AAA BB

EMP103 Peter Patter MMM NN

Teacher Foreign key

44

One-to-Many into Relational Model

Primary Key of the entity set with one mapping becomes foreign key of the entity set with many mapping.

regNonoOfSems


regNo


noOfSems

1 N

45

One-to-Many into Relational Model

regNo name address streamId

ST100 Bill Smith Xxx yyy 123

ST200 Rani Raja Mmm nnn 123

ST202 Neeta Roy Aaa bbb 124

Students


123 B.Tech 8

124 B.E. 8

Courses

ST202 Neeta Roy Aaa bbb 124

Foreign key

46

Many-to-Many into Relational Model

A new relation for relationship between the two entity sets is created. This relation will contain the attributes as primary keys of both the

entity sets. Combination of these two attributes become the primary key of this relation.

Customer owns Bank Account

acctNo

balancecustId name

address

M N

47

custId name address

C100 Bill Smith Xxx yyy

C200 Rani Raja Mmm nnn

C202 Neeta Roy Aaa bbb

Customer

acctNo balance

BankAccount

custId acctNo

Owns

Primary Key

acctNo balance

4343434 10000

4343435 20000

4343436 25000

custId acctNo

C100 4343434

C200 4343435

C202 4343436

C202 4343434

48

Relationships with attribute

Modeling relationship set with attributes: Like entity set, relationship is also translated into table.

The primary key attributes of each participating entity set, as foreign key fields.

49


dateOfJoiningdeptId

nameempId

Relationships with attribute


Location

nameaddress

capacity

locId

50

Works-InempId deptId locId dateOfJoining

EMP101 MKT BLR1 7-APR-2006

EMP102 TRA BLR2 21-JUN-2006

empId name

EMP101 Mona Lisa

EmployeesdeptId name

MKT Marketing

Departments

Together form primary key

Foreign key

EMP101 Mona Lisa

EMP102 Lora Nillie

EMP103 Peter Patter

MKT Marketing

TRA Training

DEV Development

locId address capacity

BLR1 Banashankari 100

BLR2 MG Road 50

Location

51

Modeling Key Constraints

Key Constraints is modeled as a Unique constraint.

regNoaddress

streamIdnoOfSemsDirectional arrow

Courses Has Studentsname

title

1 N

enrollment-date

Directional arrow

52

regNo name address

ST100 Bill Smith 8

Students

regNo streamId enrollment-date

ST100 123 8

ST200 124 8

ST100

Has

UNIQUE(regNo)


123 B.Tech 8

124 B.E. 8

Courses

ST100 Bill Smith 8

ST200 Rani Raja 8

ST202 Neeta Roy 6

53

Modeling Participation Constraint

Total participation constraint is modeled as foreign key with CASCADE on deletion or updation or NO ACTION is specified.

Partial participation constraint is modeled as foreign key with SET NULL on deletion or updation.

54


dateOfJoining

deptId

name

empId

location

namename

addresscapacity

locId

55

Works-InempId deptId locId dateOfJoining

EMP101 MKT BLR1 7-APR-2006

EMP102 TRA BLR2 21-JUN-2006

empId name

EMP101 Mona Lisa

EmployeesdeptId name

MKT Marketing

Departments

Foreign key with

CASCADE on delete

or update

COR

EMP101 Mona Lisa

EMP102 Lora Nillie

EMP103 Peter Patter

MKT Marketing

TRA Corporate Training

DEV Development

locId address capacity

BLR1 Banashankari 100

BLR2 MG Road 50

Location

COR

56

Modeling Weak Entity

Weak entity is modeled as foreign key with CASCADE on deletion or updation with NOT NULL constraint (if the foreign key attribute is not part-key).

57

Modeling Hierarchy

Each of entity set in the hierarchy is modeled as distinct relation.

The primary key of the child entity set is same as the primary key of the parent entity set.

The primary key of the child entity set is also foreign key referencing to its parent entity set.to its parent entity set.

The foreign key must be with cascade delete and update constraint.

58

Employeename empId

IS-A

Programmer Marketing

Current-Project

Main-Role

area

contracts

EmpId Name

Employee

EmpId contracts area

Marketing

EmpId Name

EMP1 K.Narayanan

EMP2 M.Joshna

EmpId Current-Project Main-Role

EMP1 ABC Designing

EMP2 XYZ Coding

Programmer

EmpId contracts area

EMP1 XXX Training

Foreign key

Foreign key

59

Modeling Aggregation

The aggregation relationship contains the primary key attributes as combination of all keys of the entity sets and relationships it is linked with.

The key attributes are also the foreign key. The key attributes are also the foreign key.

60

Employee

namejoiningDate

works Project

aggregation

empId

pid

startDate

uses Machinery machineID

purchaseDate

hours

Uses(empId, pid, machineID, hours)Primary Key

Foreign Key

61

Question for you?

How will you model unary relationship into relational model?

address

CustomercustId

name

referred by

62

Modeling composite attribute Each of the attributes of the composite attribute is modeled as columns

of the table. The composite attribute does not appear as a column in the table. Its

value is obtained by concatenating the values of the attributes. It appears as a column in the view.

address

house number street number

colony or area

city or towndistrict

state

country

Employees

composite attribute

empId

63

EmpId house no

street number

area or town

dist state country

EMP1 12 8th main MG rd. BLR Karnataka India

EMP2 50 2nd Main MG rd. BLR Karnataka India

Employee

EmployeeAddressView

EmpId Address

EMP1 12, 8th main, MG rd., BLR, Karnataka, India

EMP2 50, 2nd main, MG rd., BLR, Karnataka, India

EmployeeAddressView

64

Modeling Multi-Valued Attribute

A table is created for multi-value attribute containing the primary key of the entity, multi-value attribute and its corresponding attributes.

phone_numbers

Employeesmulti-valued attribute empId

name

65

EmpId Name

EMP1 Nelson Mac

EMP2 Kate Dell

Employee

EmpId Phone_Numbers

PhoneNumbers

Table for multi-valued attribute

EmpId Phone_Numbers

EMP1 9831610763

EMP1 54783990

EMP2 9831688789

EMP2 5575390

66

Modeling Derived Attribute

Like composite attribute, derived attribute is also implemented as a view.

Employee

deductionsgross_salary

net_salary

derived attribute

empId

67

EmpId Gross_Salary Deduction

EMP1 20000 2000

EMP2 15000 1000

Employee

EmpId Net_Salary

EmployeeNetSalaryView

derived attribute

Gross_Salary - Deduction

EmpId Net_Salary

EMP1 18000

EMP2 14000

derived attribute

Documents

ER_Model Presenatation