Database Design – Lecture 12

Object Oriented Database Design cont’d

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Lecture Objectives

Class Review Relationships Associations Aggregation/Composition Inheritance

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Classes

ClassName

attributes

operations()

Structure:

• Attribute names start with a small capital. If an attribute name is made up of multiple words, there is no space between the words and each subsequent word begins with a capital letter• Operation names start with a small capital. If an operation name is made up of multiple words, there is no space between the words and each subsequent word begins with a capital letter

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Classes

Class Example

Employee

nameADDRESSdobtelephoneDEPENDENT

BENEFICIARY

Address

streetNumberstreetcityprovincepostalCodeEMPLOYEE

Denotes another abstract data Type (ADT); or another class

Dependent

nameDobEMPLOYEE

Beneficiary

nameRelationshipEMPLOYEE

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Classes

Class Example (different notation)

Employee

nameaddressdobtelephonedependents

beneficiary

Address

streetNumberstreetcityprovincepostalCode

Denotes another abstract data Type (ADT); or another class

Dependent

namedob

Beneficiary

namerelationship

employee

employee

employee

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Lecture Objectives

Classes Relationships Associations Aggregation/Composition Inheritance

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Relationships 1:1 I.e. An employee has 1 address and an address belongs to 1 employee

Address

streetNumberstreetcityprovincepostalCodeemployee 1

Employee

nameaddress 1dobtelephonedependent

beneficiaryDenotes amandatoryparticipation

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Relationships 1:M I.e. An employee has 0 or more dependents and a dependent belongs to 1 employee

Employee

nameaddress 1dobtelephonedependent M

beneficiary (no line) denotes anoptionalparticipation

Dependent

namedobemployee 1

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Relationships M:N (option 1) I.e. An employee has 1 or more beneficiaries and a beneficiary belongs to 1 or more

employees

employee M

Beneficiary

namepercentrelationship

Employee

nameaddress 1dobtelephonedependent M

beneficiary M

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Relationships M:N (option 2) I.e. An employee has 1 or more beneficiaries and a beneficiary belongs to 1 or more employees Create an intersection class with associated attributes

employeeBeneficiary M

Beneficiary

name

Employee

nameaddress 1dobtelephonedependent M

employeeBeneficiary M

employee 1

EmployeeBeneficiary

percent relationship

beneficiary 1

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Relationships – two notations

Employee

nameaddress 1dobtelephonedependent M

beneficiary M

Dependent

namedobemployee 1

employee M

Beneficiary

namepercentrelationship

Note how we can show M:N relationship in OODM

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Lecture Objectives

Classes Relationships Associations Aggregation/Composition Inheritance

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Associations An association between two classes indicates

the possibility that links will exist between the objects of the classes

The links provide the ability for message passing to happen

Links can be uni-directional or bi-directional associations as well as more complex type links such as aggregation/composition – need to clearly understand the navigability of the association

Links also show multiplicity (1:1; 1:M; M:N)

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Associations

1:1 Can be bi-directional or uni-directional

which shows the direction a message can be sent

Bi-directional – message goes in both directions

Address

streetNumberstreetcityprovincepostalCodeemployee 1

Employee

namedob

address 111 Lives at

Bi-directional; message goes in both directions

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Associations

1:1 Uni-directional – message goes in direction

of arrow only Note there is no reference to the Employee

class in the Address classAddress

streetNumberstreetcityprovincepostalCode

Employee

namedob

address 11Lives at

Uni-directional; message goes in one direction only

**Note there is no reference to employee abstract data type (ADT) in the Address class

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Associations

1:M Can be bi-directional or uni-directional What would change if we made it a uni-

directional association?Employee

nameaddress 1dobtelephonedependent M

beneficiary

Dependent

namedobemployee 1

1 0..nCan have

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Associations

1:M Can be bi-directional or uni-directional What would change if we made it a uni-

directional association? – see belowEmployee

nameaddress 1dobtelephonedependent M

beneficiary

Dependent

namedobemployee 1

0..nCan have **Note there would be no reference to employee abstract data type (ADT) in the Dependent class

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Associations

M:N Can be bi-directional or uni-directional What would change if we made it a bi-

directional association?Employee

nameaddress 1dobtelephonedependent M

beneficiary M

Beneficiary

namerelationship

1..nCan have

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Associations

M:N Can be bi-directional or uni-directional What would change if we made it a bi-

directional association? – see belowEmployee

nameaddress 1dobtelephonedependent M

beneficiary M

Beneficiary

namerelationship

employee M

1..n 1..nCan have**Note a reference to employee abstract data class would be added

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Lecture Objectives

Classes Relationships Associations Aggregation/Composition Inheritance

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Aggregation/Composition A special kind of association. A whole (assembly) –part (components)

relationship An instance of one class may consist of, or

include instances of another class. The aggregate class assumes a special role for

delegation of responsibility and leadership The number of ‘parts’ are shown by multiplicity Aggregations are usually 1-to-many (aggregate

to components) but not always

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Aggregation/Composition A “has a” or “consists of” relationship A Book contains Chapters

Book Chapter

contains

Aggregate or whole Components or part

Diamond symbol denotes an aggregation

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Aggregation/Composition

Example: An invoice has invoice items A car has tires A company has contacts

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Aggregation/Composition Composition is a special kind of aggregation. The component parts depend on the

aggregate for existence—delete the aggregate and the components disappear

Book Chapter

contains

Aggregate or whole Component or part

Filled in diamond symbol denotes a composition

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Aggregation vs Association

Which of these are composition? An invoice has invoice items A car has tires A company has contacts

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Aggregation vs Association

Show compositions in OODM only – aggregations can be shown as associations only

If you are not clear on the relationship between two classes, assume it is only an association – do not assume it has to be aggregation, composition or inheritance!

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Lecture Objectives

Classes Relationships Assoications Aggregation/Composition Inheritance

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Inheritance

Classes are organized into a hierarchy Hierarchy equates to inheritance Inheritance allows an object to inherit

the data structure and behavior of the classes above it

In OO systems, all objects are derived from the super class Object or the Root class

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Inheritance

Single Inheritance (~Hierarchical Structure)

A class has only one immediate (parent) superclass above it

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Inheritance

Multiple Inheritance (~Network Structure)

A class has more than one immediate (parent) superclass above it

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Inheritance

Defining Inheritance Two approaches:

Generalization Look for common attributes and operations in a

set of classes and create a new superclass and place the common attributes and operations into the superclass

Specialization Create two or more subclasses to associate

attributes and methods to

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Inheritance

Defining Inheritance Generalization

Look for common attributes and operations in a set of classes and create a new superclass and place the common attributes and operations into the superclass

Two classes that share common attributes and operations create a new class called StaffMember and move common attributes and operations to new superclass

+calculateBonus()

-name-address-qualification

CreativeStaff

+calculateBonus()

-name-address

AdminStaff

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Inheritance

Generalization

+calculateBonus()

AdminStaff

+calculateBonus()

-qualifications

CreativeStaff

+calculateBonus()

-name-address

StaffMember

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Inheritance

Defining Inheritance

Specialization

One class however, it may be determined that there are different types of staff members resulting in the creation of some sub classes

+calculateBonus()

-name-address

Staff

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Inheritance

Defining Inheritance

Specialization

+calculateBonus()

AdminStaff

+calculateBonus()

-qualifications

CreativeStaff

+calculateBonus()

-name-address

Staff