its232 introduction to database management systems
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ITS232Introduction To Database Management Systems
Siti Nurbaya IsmailFaculty of Computer Science & Mathematics,
Universiti Teknologi MARA (UiTM), Kedah| sitinurbaya@kedah.uitm.edu.my | http://www.sitinur151.wordpress.com |
| A2-3039 | ext:2561 | 019-5710562 |
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
3
Chapter 4: Entity Relationship (E-R) ModelingBasic Modeling Concept
A model is description or analogy used to visualize something that cannot be directly observed.
Chapter 4: Entity Relationship (E-R) ModelingBasic Modeling Concept
4
• 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.
Chapter 4: Entity Relationship (E-R) ModelingBasic Modeling Concept
5
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
Chapter 4: Entity Relationship (E-R) ModelingBasic Modeling Concept
6
The importance of data modeling:
Data Application
View 1
View 2
View n
Model
holistic view of the same data
Chapter 4: Entity Relationship (E-R) ModelingBasic Modeling Concept
7
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
8
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
Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model
9
• 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
10
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
Chen Model Crow’s Foot Model
STUDENT SUBJECT STUDENT SUBJECT
Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model: Entity
11
Entity• An entity is a thing that exists and can be distinguishable
• concrete/physical (individual, place, object)• conceptual/abstract (events, concepts)
• Examples;• Jeffry, 2009222624 STUDENT• Mathematics II, MAT111 SUBJECT
• Have property that can explains about the entity• Entity set a set of entity
Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model: Attribute
12
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 Crow’s Foot Model• attributes are represented by
ovals and are connected to entity rectangle with a line
• each oval contains the name of attribute it represents
• attributes are written in attribute box below entity rectangle
Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model: Attribute
13
Chen Model Crow’s Foot Model
STUDENT
studentID
name
course
SUBJECTcodecreditname
STUDENT
studentIDcoursename
SUBJECT credit
name
code
Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model
14
Chen Model Crow’s Foot ModelERD
TABLE
RATIONALSCHEMA
STUDENT(studentID, name, course)SUBJECT(code, name, credit)
STUDENT
studentID
name
course
SUBJECT
codenamecredit
STUDENT
studentIDnamecourse
SUBJECT credit
name
code
studentID name course
………………… ……… ……………
code name credit
……………
……………… ……………
STUDENT SUBJECT
Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model: Relationship
15
Relationship• Associates between entities• Logical interaction among the entities in a relational database • Operate in both directions
Chen Model Crow’s Foot Model• Weak Relationship
• Strong Relationship
• Weak Relationship
• Strong Relationshipworkshas
works
has
works
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram
16
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
17
Chen Model Crow’s Foot ModelENTITY
ATTRIBUTE
RELATIONSHIP
STUDENT STUDENT
STUDENT
studentID
name
course
STUDENTstudentIDcoursename
works works
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Model Components
18
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
19
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
STUDENT
studentID
name
courseemail
address
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity
20
Variations of Entity:i. Weak Entityii. Recursive Entityiii. Composite Entityiv. Entity Supertype and Subtype
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity
21
Variations of Entity:i. Weak Entity
• Existence dependency• Primary key derived from parent entity• Example: DEPENDENT entity
EMPLOYEE(employeeNO, employeeNAME)DEPENDENT(employeeNO, depNO, depDATE, depNAME)
EMPLOYEE
employeeNO
employeeNAME DEPENDENTDEPENDENT
employeeNO
depNAME
depDATE
depNO
has1(0,N)
1(1,N)
employeeNO employeeNAME111 Ali222 Ah Chong333 Bazil
employeeNO depNO depNAME depDATE111 1 Zara 05/05/05111 2 John 25/12/09333 3 Syamil 28/10/09333 1 Jazmeen 01/01/11
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity
22
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
11
employeeSPOUSE
EMPLOYEEemployeeNO
employeeNAME
manage
11
employeeMANAGER
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity
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
1 1
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity
24
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
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity
25
Variations of Entity:iv. Entity Supertype & Subtype
• Example: Superype (EMPLOYEE) Subtype (Engineer & Full-Time)
Employee(emp_no, emp_name)Manager(emp_no, emp_name,bonus)
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity
26
Variations of Entity:iv. Entity Supertype & Subtype
• 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
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity
27
Variations of Entity:iv. Entity Supertype & Subtype
• Example: Disjoint & Overlap
Overlap
Disjoint
G
Gs
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity
28
Variations of Entity:iv. Entity Supertype & Subtype
• Example: Disjoint
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity
29
Variations of Entity:iv. Entity Supertype & Subtype
• Example: Disjoint & Overlap
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes
30
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
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes
31
Attributes types:i. Simple Attributesii. Composite Attributesiii. Multivalued Attributesiv. Derived Attributes
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes
32
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
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes
33
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
STUDENT studentIDphoneNO
age
gendername
address addressTOWN
addressPOSTCODEaddressNO
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes
34
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
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes
35
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
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes
36
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.
• Should not implement derived attributes in relational database• Example: age, cgpa
Derived Attributes
STUDENT studentIDphoneNO
age
gender
name
address
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship
37
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
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship
38
Relationship is described 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: Relationship
39
Relationship is described by:i. Degree of the relationship
• Indicates number of associated entities within the relationship• There are three types:
a.Unary Relationship
b.Binary Relationship
c. Ternary Relationship
STAFF married
LECTURER teach CLAS
CANDIDATE teach INTERVIEW
MANAGEMENT
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship
40
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
11 M N
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship
41
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
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship
42
Relationship is described by:iii. Cardinality of the relationship
• Example 1:One student can register 1 to 9 coursesOne course maximum can have 35 student
(1,9) (0,35)STUDENT register COURSENM
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship
43
Relationship is described by:iii. Cardinality of the relationship
• Example 2:One lecturer can teaches maximum 3 coursesOne course can be thought by 1 lecturer only
(0,3) (1,1)LECTURER teach COURSEM1
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:iii. Cardinality of the relationship
• Relationship Strength Existence Dependence• Entity’s existence depends on the existence of one or more other
entities
namestaffNO
STUDENT
namestudentID
staffNO*refer
supervise
SUPERVISORstaffNO
name______ __________ ____
STUDENTstudentID name staffNO________ ____ ______________ ____ ______
referSUPERVISOR
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:iii. Cardinality of the relationship
• 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 45
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship
Relationship is described by:iv. Participation
• Determines whether all or some entity occurrences participates in a relationship
• There are two types:a. Optional (Partial)
Condition in which other participating entity may or may not be associated with occurrences of the optional entity in the relationship
b. Mandatory (Total) Condition in which one participating entity must be
associated with one or more occurrences of the other participating entity in the relationship 46
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship
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
48
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
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Comparison of E-R Model
M
Summary of Cardinality and Participation for a Strong RelationshipCardinality & Participation Chen Model Crow’s Foot Model
1:1, both side mandatory
1:M, both side mandatory
M:N, both side mandatory
1:1, both side optional
1:M, both side optional
M:N, both side optional
1:M, one side mandatory and many side optional
has1 1(1,1) (1,1)
has1 M(1,n) (1,1)
hasM N(1,n) (1,n)
has1 1(0,1) (0,1)
has1 M(0,n) (0,1)
hasM N(1,n) (0,n)
has1 M(0,1) (1,1)
has
has
has
has
has
has
has
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Comparison of E-R Model
Chen Model
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Comparison of E-R Model
Crow’s Foot Model
Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Comparison of E-R 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
53
Chapter 4: Entity Relationship (E-R) ModelingExercise 1
54
• An employee manages one store; each store is managed by one employee
• Answers
manageEMPLOYEE STORE1 1
Chapter 4: Entity Relationship (E-R) ModelingExercise 2
55
• A painter can paint many paintings; each painting is painted by one painter. A gallery can have many paintings. A painting can be exhibited by a gallery.
• Answers:
PAINTER PAINTING GALLERYpaint displayM1 1M
Chapter 4: Entity Relationship (E-R) ModelingExercise 3 (a):
56
• Students in Morris College discover that each course can have many sections, but each section refers to only one course.
• Answers
hasCOURSE SECTION(0,N)(1,1)
M1
Chapter 4: Entity Relationship (E-R) ModelingExercise 3 (b):
57
• Each student in Morris College can take many classes (or none) and each class can contain many students.
• Answers:
takeSTUDENT
(0,N)
(1,M)
M
N
CLASS
Chapter 4: Entity Relationship (E-R) ModelingExercise 3 (c):
58
Apply business rules in exercise 3(a) & 3(b).• Students in Morris College discover that each course can have many
sections, but each section refers to only one course. • Each student in Morris College can take many classes (or none) and
each class can contain many students.(class and course in Morris College refer to the same entity)
takeSTUDENT
(0,N)
(1,M)
M
N
hasCOURSE CLASS(0,N)(1,1)
M1
Chapter 4: Entity Relationship (E-R) ModelingExercise 3 (d):
Apply business rules in exercise 3(a) & 3(b).• Students in Morris College discover that each course can have many
sections, but each section refers to only one course. • Each student in Morris College can take many classes (or none) and
each class can contain many students.(class and course in Morris College refer to the same entity)
• Some course in Morris College may have prerequisite course.• Students will have enroll grade for every course they have taken.
hasM1
takeSTUDENT
(0,N)
(1,M)
M
N
COURSE CLASS(0,N)(1,1)
prerequisite
grade
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