its232 introduction to database management systems

ITS232Introduction To Database Management Systems

Siti Nurbaya IsmailFaculty of Computer Science & Mathematics,

Universiti Teknologi MARA (UiTM), Kedah| [email protected] | http://www.sitinur151.wordpress.com |

| A2-3039 | ext:2561 | 012-7760562 |

CHAPTER 4Entity Relationship (E-R) Modeling

(ERD)

4.0 Entity Relationship (E-R) Modeling4.1 The Entity Relationship (ER) Model 4.2 Developing An E-R Diagram 4.3 Database Design Challenges

Chapter 4: Entity Relationship (E-R) Modeling

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Chapter 4: Entity Relationship (E-R) ModelingBasic Modeling Concept

A model is description or analogy used to visualize something that cannot be directly observed.


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• Relatively simple representations of complex real world data structures

• Represents:– data structures and their characteristics– relation and constraints

• Can be physical or abstract:– car, student = physical– subject, register= abstract

• Used by database designer as:– communications tools to communicate and understanding

between a client and the database designer, which the database to be develop.


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The importance of data modeling:

• Data– constitute the most basic information units employed by a system

• Application – is created to manage data and to transform data to information

• View– different people views the same data differently based on their

understanding• Model

– helps different user to have the holistic view of the same data


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2. Conceptual level

3. Internal level

Physical data organization

1. External level View 1 View 2 View n

Conceptual Schema

Internal Schema

Database

User nUser 2User 1

…

Conceptual Model

External Model

Internal Model

Physical Model

-designer’s view-h/w independent-s/w independent

-DBMS’s view-h/w independent-s/w dependent

-h/w dependent-s/w dependent

-user’s view

ERD

Three Level ANSI-SPARC Architecture

Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model

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Based on the set theory and the relational theory, it is used as tools to:– translate different views of data among managers, users and

programmers to fit into a common work– define data processing and constraints to help meet the different

views– help implement the database– considered as a stage in a database design preceding the relational

database modeling– gives data structures representation of:

* what information have to be stored* the relationships between informational elements and

constraint on the data structure * relationship


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• ER model forms the basis of an ER diagram (ERD)• ERD represents conceptual database as viewed by end user• ERDs depict database’s main components:

– Entities– Attributes– Relationships

Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model: Entity

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Entity• Refers to entity set and not to single entity occurrence• Corresponds to table and not to row in relational environment• In both Chen and Crow’s Foot models, entity is represented by

rectangle containing entity’s name• Entity name, a noun, is usually written in capital letters

Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model: Attribute

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Attribute• Characteristics of entities• Property that explains about entity• Correspondents to fields of a table• Primary key are underline with a straight line• Foreign key are underline with dotted line or an *• Chen Model

• attributes are represented by ovals and are connected to entity rectangle with a line

• each oval contains the name of attribute it represents

• Crow’s Foot Model• attributes are written in attribute box below entity rectangle


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The Attributes of the STUDENT entity: Chen & Crow’s Foot

Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model: Relationship

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Relationship• Associates between entities• Logical interaction among the entities in a relational database • Operate in both directions• Chen Model

• Crow’s Foot Model

Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram

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Development of ER model is an Iterative Process that involved:• Step1:

General narrative of organizational operations developed• Step2:

Basic E-R Model graphically depicted and reviewed• Step3:

Modifications made to incorporate newly discovered ER components

• Repeat process: Until designers and users agree on complete E-R Diagram

Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Model Components

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ENTITY Variations of entity:i. Weakii. Recursiveiii. Compositeiv. Supertype/Subtype

ATTRIBUTE Types of attribute:i. Simple attributesii. Composite attributesiii. Multivalued attributesiv. Derived attributes

RELATIONSHIP Relationship can be describes by:i. Degree of the relationshipii. Connectivity of the relationshipiii. Cardinality of the relationshipiv. Participation

Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity

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Entity• Corresponds to table and not to row in relational environment• Represented by rectangle containing entity’s name• Entity name, a noun, is usually written in capital letters• Examlpe: Entity STUDENT with attributes


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Variations of Entity:i. Weak Entityii. Recursive Entityiii. Composite Entityiv. Entity Supertype and Subtype


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Variations of Entity:i. Weak Entity

– Existence-dependent– Primary key partially or totally derived from parent entity in

relationship– Database designer determines whether an entity is weak based

on business rules


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Variations of Entity:ii. Recursive Entity

• Entity set that have relationship with the same entity set• Example: EMPLOYEE entity

employeeNO employeeNAME employeeSPOUSE111 Ali 444222 Ah Chong333 Bazil444 Sheriz 111

employeeNO employeeNAME employeeMANAGER111 Ali 333222 Ah Chong 333333 Bazil 333444 Sheriz

EMPLOYEEemployeeNO

employeeNAME

married

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employeeSPOUSE

EMPLOYEEemployeeNO

employeeNAME

manage

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employeeMANAGER


Variations of Entity:iii. Composite Entity

• Originally a relationship between 2 entities that involved in M:N relationship

• Composite entity takes its primary key from both entities that it bridges

• Example: enroll

studentID studentNAME200922222200933333200944444200955555

courseID courseNAMEITS232 DatabaseCSC318 IPCSC203 OS

STUDENTstudentID

studentNAME

enrollM

grade

COURSE courseID

courseNAME

N

studentID courseID grade200922222 ITS232 A+200922222 CSC318 B+200933333 CSC203 B200955555 ITS232 A-

STUDENT STUDENT_COURSE / ENROLL COURSE


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Variations of Entity:iv. Entity Supertype & Subtype

• Parent-Child relationship

• Supertypecontains the shared attributes an entity type that include distinct subclasses

that required to be presented in data model parent

• Subtype contains the unique attributesan entity type that has a distinct role and also

a member of supertypechild


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• Example: Superype (EMPLOYEE) Subtype (Engineer & Full-Time)


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• Have two types of relationship:Disjoint Overlapping

Unique subtypeNon-overlapping: subtypes can be one of the types

Overlapping:Subtypes can be either one or both of the subtypes

Indicate with: Indicate with:

G Gs


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• Example: Disjoint & Overlap

Overlap

Disjoint

G

Gs


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• Example: Disjoint


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• Example: Disjoint & Overlap

Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes

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Attributes• Represented by ovals that are connected to entity with a line• Oval contains of attribute (field) it represents• PK are underlined with straight line• FK are underlined with doted line or *• Example: Entity STUDENT with attributes

name, course, studentID, address, email

STUDENT

studentID

name

courseemail

address


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Attributes types:i. Simple Attributesii. Composite Attributesiii. Multivalued Attributesiv. Derived Attributes


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Attributes types:i. Simple Attributes

• An attribute composed of single component with an independent existence

• Cannot be subdivided into smaller components• Example: gender, martial statues

STUDENT studentIDphoneNO

age

gendername

address addressTOWN

addressPOSTCODEaddressNO

Simple Attributes


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Attributes types:ii. Composite Attributes

• An attribute composed of multiple components, each with an independent existence

• Can be further subdivide to yield additional attributes• Example: name first, middle, last

address street, city, state, zip

Composite Attributes


age

gendername

address addressTOWN

addressPOSTCODEaddressNO


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Attributes types:iii. Multivalued Attributes

• attribute that holds multiple values for each occurrence of an entity type

• Should not be implemented multivalued attributes in relational database

• Can simplifies multivalued attributes by:a. Create several attributesb. Create new entity of the original multivalued attributes

components• Example: phone number handset,office,homequalification diploma,degree,master


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Attributes types:iii. Multivalued Attributes

• Can simplifies multivalued attributes by:a. Create several attributes

b. Create new entity of the original multivalued attributes components

gender

STUDENT

studentID

handsetNO

age

address

CONTACThas

homephoneNO

studentID*

STUDENTage

gender

address

handsetNO

homephoneNOstudentID


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Attributes types:iv. Derived Attributes

• An attributes that represents a value that is derived from the value of related attribute or set of attributes, not necessarily in the same entity type.

• Need not be physically stored within database• Example: age, cgpa

Derived Attributes


age

gender

name

address

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Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship

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Relationship• Associations between entities • Logical interaction among the entities in a relational database• Operates in both directions• Naming Relationships:

• Relationship name is a verb phrase• Avoid vague names

• Defining Relationships:• Definition explains what action is being taken and why it is important• Give examples to clarify the action• Optional participation should be explained• Explain reasons for any explicit maximum cardinality• Explain any restrictions on participation in the relationship• Explain extent of the history that is kept in the relationship• Explain whether an entity instance involved in a relationship instance can

transfer participation to another relationship instance


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Relationship is described by:i. Degree of the relationshipii. Connectivity of the relationshipiii. Cardinality of the relationshipiv. Participation


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Relationship is described by:i. Degree of the relationship

• Indicates number of associated entities within the relationship• There are three types:

a.Unary Relationship• Association is maintained within single entity

b.Binary Relationship• Two entities are associated

c. Ternary Relationship• Three entities are associated


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Relationship is described by:ii. Connectivity of the relationship

• Logical interaction among entities in a relational database• There are three types:

a.1:1

b.1:M

c. M:N

STUDENT under PROGRAM

UiTMBRANCH have RECTOR

STUDENT register COURSE

1 1

1 M

N1 M


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Relationship is described by:iii. Cardinality of the relationship

• Express the specific number of entity occurrences associated with one occurrence of the related entity

• Function of organizational policy business rules


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• Example 1:One student can register 1 to 9 coursesOne course maximum can have 35 student

(1,9) (0,35)STUDENT register COURSENM


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• Example 2:One lecturer can teaches maximum 3 coursesOne course can be thought by 1 lecturer only

(0,3) (1,1)LECTURER teach COURSEM1

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• Example 3:




• Relationship Strength Existence Dependence

– Existence dependence• Entity exists in database only when it is associated with another

related entity occurrence– Existence independence

• Entity can exist apart from one or more related entities• Sometimes such an entity is referred to as a strong or regular

entity



• From Existence Dependence, exist two relationship strength:a. Weak Relationship

Entity not existence-independent on other entity PK of related entity doesn’t contain PK component of parent

entity Non-Identifying Relationship

b. Strong Relationship Existence dependence PK of related entity contains PK component of parent entity Identifying Relationship 46

Database Systems, 9h Edition 49


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Relationship is described by:iv. Participation

• Determines whether all or some entity occurrences participates in a relationship

• There are two types:a. Optional (Partial)

• One entity occurrence does not require corresponding entity occurrence in particular relationship

b. Mandatory (Total)• One entity occurrence requires corresponding entity

occurrence in particular relationship

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Relationship is described by:iv. Participation

• Example 1:One lecturer can teaches maximum 3 coursesOne course can be thought by 1 lecturer only

(0,3) (1,1)LECTURER teach COURSEM1

connectivity

cardinality

One class can be thought by one lecturer only

One lecturer can teachesmaximum 3 classes

participation

‘not all lecturer teach class’ optional participation for course

‘all class are teach’ (mandatory participation for lecturer)

Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Comparison of E-R Model

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Alternate style developed to enable easier use of CASE tools.

Chen ModelThe Chen notation favors conceptual modeling

Crow’s Foot ModelCrow’s Foot notation favors a more implementation-oriented approach

UML ModelUML notation can be used for both conceptual and implementation modeling

Comparison of E-R Modeling SymbolsCardinality & Participation Chen Model Crow’s Foot Model

Entity

Weak Entity

Composite Entity

Relationship line

Relationship

Option Symbol

One (1) Symbol

Many (M) Symbol

1


M

Chen Model


Crow’s Foot Model


Chapter 4: Entity Relationship (E-R) Modeling4.3 Database Design Challenges

Conflicting Goals• Database designers often must make design compromises that are

trigged by conflicting goals, such as comply with the design standards, processing speed and information requirements.

• In order to do so, – it is very important to have the entities, attributes, and

relationships clearly identified and well-defined– there is a need in balancing between the customer needs and a

design that meets logical requirements and conventions– The more thinking and modeling is done the less money and

time are needed later on for rework

• Additional concerns are security, performance, shared access and integrity

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its232 introduction to database management systems

Documents

entity relationship

er diagram

data structure relationship

conceptual database

data processing

importance of data modeling

database designer

different views of data